Suggesting there's just one way to fight is wrong. There are different ways to approach various bosses and enemies, and some techniques work better than others against specific bosses.
The general rules to an encounter remain the same: "The Bodyguard takes the damage, The Hunter makes the damage, and the Doctor heals the damage."
The method in which you apply this will always depend upon your target. It's a good idea to look at the Aggro page and get familiar with the various ways on how bosses/enemies act, to understand what tactics are going to work against it.
There's also your character class, and group strength's and weaknesses that will determine the best tactic to use for each boss.
Gear Plays a RoleEdit
It's not just a class thing, the bonuses attached to equipment, weapons and gear, makes a difference with where your character's strengths and weaknesses are.
Attributes, do they do what you think they do?Edit
Ranged power is described as being a bonus to the damage your ranged weapon will make. However, that's not all it does.
It also helps define how many points of healing a Doctor will make when using the Quick Heal skill. However, only the initial cast is affected by range power, not the heal-over-time ticks. Roughly, +100 armor adds +20 to Quick Heal.
Melee power is described as being bonus damage to melee hits, however, what else does it affect?
Melee Power also affects a doctor's Group Heal.
Also Melee Power increases the amount of white damage dealt, even when using range weapons. Currently, range power does not increase white damage, not even for hunters. In this sense, melee power is preferred over range.
It's not hard to see how they might affect the skills of other classes. For example, would ranged power affect the ability of a Bodyguard to taunt?
Tip: A Bodyguard should focus on maximizing their Armor bonuses first, and then Melee (for solo ventures and PVP) or Health levels. The health bonus is good for making the BG/Doc formula work; It can make up the difference between a good and great doctor.
A truly perfect bodyguard will hold appropriate equipment for group, and non-group use. Although Health bonuses are recommended for group use, if there's a great doctor in the group, the BG/Doc formula has already been achieved, so the Bodyguard can focus on delivering more damage with his Melee focused equipment.
At this stage in time...Edit
The following suggestions on gear may not be optimal. Experience is easy to come by, and players will find themselves leveling faster than they can craft, even for white items. However, this may still be subject to change.
Crafting gear can take some time. As noted elsewhere, there are white, green, blue(rare), and purple(epic), items.
From level 1 to level 5, you should strive to get as much gear as possible to fill your wearable equipment slots. Just fill them up.
From level 5 to 10 you should be trying to get as much green gear as you can.
From 10 to 20, you should always strive to have, at a minimum, all green items that are within two or three levels of your current level, but hopefully, you'll also acquire some blue items too.
From 20 to 29 you should be trying to get as much blue as possible, with hopefully a purple or two.
At level 30, and the prestige levels, you need to try and get to all purple as quickly as possible. Boss Drops tend to be stronger than what's in the store, but they're more work (sometimes many repeated boss runs). However, some boss dropped plans don't require Boss components at all, and yet offer similar (sometimes identical) stats. Take a look at the Boss drop page, and make a plan.
A good strong Bodyguard/Doctor formula typically means that "tanking" is preferred, depending upon the boss, but sometimes it's better to just try to avoid most of the boss damage and kite them instead.
Tip: You should never hit any target before the Bodyguard has a chance to grab aggro on that target, otherwise they'll have to fight the aggro you gained, which on some bosses, can be extremely difficult to do. You should also avoid healing or skill actions that might grab aggro before the Bodyguard can.
The Bodyguard/Doctor formula is the equation that basically determines how long the group can sustain an encounter. The basic idea is a great Bodyguard can be successful long-term if teamed with a decent Doctor. A great Doctor can be successful long-term with a decent Bodyguard. The Hunters also enter into this.. A great hunter, will enable a doc to heal more often (hunter energy spike skill), AND enable the encounter to be shorter (through damage dealt, and/or smooth moves being used on the group). So in effect, a decent Hunter will improve a doctor, which is why it's called the BG/Doc formula, and not the BG/Doc/Hunter formula.
A bad bodyguard with lousy gear NEEDS a great doctor and a good hunter can improve a good doctor to a great one. A bad doctor will typically spell failure, regardless of the other group members. A bad hunter can still enable a good group to survive.
The actual "optimum mix" always depends upon the environment, the boss(es) in question, and the player skills. Typically speaking though, an extra doc is always considered to be good luck, as long as the hunter can keep up energy spikes. An extra Bodyguard can often feel like a third wheel, but can be useful with adds, or with taking over boss aggro if the primary bodyguard goes down. An extra Hunter is a lot of fun, especially if you have a great team established.
This is pretty straightforward; usually the Bodyguard runs straight up to the boss, grabs aggro, and begins a toe-to-toe melee assault on the boss. They should at least consider using forcefields to increase their armor, but should always ensure that they are using their "Harden" skill every time it's available. Bodyguard tanks should also ensure that they taunt or use aggro skills repeatedly to keep the boss's interest.
Between a rock and a hard place
The best way to tank is to lure a target into a corner, away from wherever the adds spawn from. Some bosses may have a door trick where they can be separated from their adds. (Note: the developers don't like door tricks, and have worked to eliminate them.)
The next consideration is that the Tank should have it's back to something. Many bosses are able to use knock back skills, so if there's nothing behind the Tank, they will get continuously pushed away and have to stand up again and then run back to start hitting the boss again. Plus the fight could move into an area where additional "sleeping" enemies are located. The easiest way to control this is to simply get between the boss and a barrier of any kind that stops the Tank from being pushed away.
Other members of the group need to position themselves out of immediate danger. Some of the attacks a boss will use have an "area effect" to them, such as knock down, stun, or burn damage from bazookas, etc. It's better to stay out of that area. If you have a mercenary, you should also do what you can to position them away from them too.
Buff's like group healing from the doctor, or a special item like "Group Energy Surprise" with an area of effect, should be done by everyone moving close to the Bodyguard, triggering the event, and then moving away again. If timed carefully, the others in the group will hopefully avoid being hit by the boss.
Kiting is where you have one person get the boss's attention, and then run like hell, trying not to get hit, while everyone else in the group takes shots at the boss. In other words, the idea is to keep out of reach of the boss's melee attacks, while enticing him to try and get into position to melee. If a boss is mainly a shooter, it becomes difficult (but not always impossible) to kite them.
Sometimes, it's still important to kite a shooter, just because it's less damage than the boss's melee attacks. On a melee boss, they will try to get within range to melee you. Distance is important. The "Smooth Moves" skill from the hunter of the group can help a Bodyguard stay ahead of faster bosses. The bodyguard has a similar skill they can use on themselves as soon as "Smooth Moves" wear off. There is also a short duration Special Items booster that will enable a speed increase. Knock backs, slow downs, and stun attacks DO affect bosses slightly, but not as noticeably as they would against normal enemies.
If the boss get's too close and warms up their melee attack, it's time to dodge, change direction, or maximize distance from the boss. On some bosses, there's nothing you can do. Some Bot bosses can perform a stomp maneuver that will cause serious damage no matter what you do, or how far away you get (unrealistically). However, some bosses will miss you (or cause less damage) if you change your direction by 45 degrees. Others will miss you if you turn 90 degrees, BUT it takes some experimentation to see which works best on which boss, because sometimes the damage depends on your absolute distance from the boss attack itself, in which case running straight away is your best option.
Typically, you'd run in a circle, but it really depends on the boss, and the environment layout. Try to get your group into the center of the path, or off to one side of the path. As the boss gets pulled around and the line-of-sight is broken between the boss and the shooters of the group, the group will automatically relocate to a position where they can shoot again, but this might pull them into bad positions. This also happens with shorter ranged weapons when the boss is pulled too far away.
Try not to run over your groupmates with the boss. This isn't always a big deal, but some enemies will attempt to use a stomp attack (or other area attack) on your group if it's drawn too close, and/or the aggro level has shifted. A little distance is nice because sometimes the bodyguard can regain aggro before the boss reaches their new target. Care must be taken at the corners of your path, because this is where the boss will come the closest to the kiter. A smooth, gradual turn will sometimes help keep the boss far enough away to avoid this. A sharp turn will almost guarantee that the boss will catch-up unless you're looping around the edge of an obstacle.
A good group knows that the corners are potential trouble spots, and might try to assist the bodyguard (and doctor) at those points with any appropriate skills or special items to slowdown the boss, or speed up the kiter.
Bodyguards should regularly use their taunt skill against the boss. This is somewhat tricky during kiting as you must stop running briefly in-order to use it. The actual taunt works faster than the animation though, so if you get the taunt animation started, and then continue running, it will still work. A quick verification to make sure the Taunt skill is in cooldown mode, will tell you if you successfully used it or need to stop longer to fire it off.
Dealing with AddsEdit
When "Adds" (additional enemies that spawn into a boss fight) appear, it's important to have a plan for dealing with them. If you're tanking "comfortably" with health not dangerously falling away, then the best solution is to have the Tank gain aggro on the newcomers too. The same goes for if you're kiting comfortably.
If the Adds are shooters, this might pose a problem, or if the doctor/bodyguard formula is weak, it may be necessary for someone else to try to grab aggro and/or deal with those adds. Typically, it becomes the job of the hunter, who would use their skills to keep the adds away and eliminate them with only slight injury to themselves.
Regardless, the plan needs to be communicated, or everyone will go after adds, and the bodyguard will try to grab aggro on them while everyone's busy trying to use knock back against them. It's also important to try and get EVERYONE to focus on eliminating the weakest target first. Usually that's an add, though the bodyguard needs to make sure they don't lose aggro on the boss.
Boss Aggro issuesEdit
As noted above, taunts and aggro attacks are typically needed in such a way that the aggro level continues to build. (See aggro for more details). If the bodyguard loses aggro, things start to get ugly fast.
Be warned though.. Some bosses don't require additional taunts unless they get ready to go after someone else (the SPARTAN bot does this when kited). You can taunt until you're blue in the face, but it wont mean a thing until the Spartan has stopped moving forward, and/or has started a stomp attack. At that point, the aggro table is reset to zero, and the boss selects a new target.
To combat this kind of behavior and recapture aggro (at least on this specific boss) the entire group should stop attacking the bot and stand still, including the one being pursued. The bodyguard needs to be the only one moving, and needs to taunt plus do aggro attacks until it chases them again.
The Lava Ant is another interesting boss, every now and then it'll chose a new target. A Bodyguard can win back aggro instantly with a single taunt. So when kiting this boss, it's a good idea to taunt every now and then, but try and have the taunt ready to use, just in case.
During an encounter, sometimes the BG/Doc formula can fail, leaving the group without a bodyguard who can handle the boss damage. If that's the case, "kiting" might keep the remaining characters alive long enough for the Tank and/or the Doctor to return to the area when they respawn.
Some players have strategies that they're willing to share, If you have a strategy for specific bosses, or perhaps PVP, please consider making a page for them and linking to them from here: Boss Strategies