For me it's generaly like this (provided that it's a hard boss):

Me:

• DOT damage - place DOT on the boss, run around until it wears, repeat

• Summoner - run around, renewing summons and debuffs on the boss

• Otherwise - do damage, drink potions if low on hp, run around until it will cooldown if I'm drinking potions too often

Boss:

• Bad Status (like reflection) - move away from him, wait

• Bad Pool - move out of it, continue from another place

• Shotgun Effect (multiple projectiles striking at once) - be ready to immediately teleport or rush away if struck. Try to predict next strike to avoid it.

Details may wary - summoner may run almost constantly, but blademaster will just break contact for a couple of seconds at most. I usually try to battle only one boss at a time, if they are multiple (Valbury). And I'll use other monsters as a source of HP (life leaching) or as a targets, I can rush to. I didn't play retaliation builds, so I never try to facetank whole battle, unless boss is very easy for me - it leads to becoming relaxed and inattentive, to missing some nasty effect (like a "bad pool") and dying as a result.