@Welldead to increase your boomkin dps you need to concentrate on managing eclipse uptime and minimizing movement, which for me takes three things, in rough order of importance:
(a) Eclipse timing: most sites say be in solar for AOE, but the trick really is working out how to do that for each fight. Your first choice of nuke will determine your eclipse rotation for the entire fight. So test both directions out and find out which one lines up best with AOE situations. You HAVE to be in solar for them, even if it means casting the wrong nuke to stay there.
(b) Knowledge of the fight and where you need to be, our movement sucks, if you have to move suddenly your dps plummets but you have a window everytime you refresh dots to move a few steps in the right direction. Get used to planning where you will be as far in advance as possible. Also cat shift and use stampeding roar or dash if you have to move far. (this I think has the largest effect, downtime or uncertainty moving differentiates low DPS players from high DPS players)
(c) DOT Timers: find and config a good DOT timer to track your DOTs, I recommend TidyPlates for multi-target and there are a million ones for single target ( i like HUDs so I use IceHUD). For AOE plant shrooms, Sunfire everything, shrooms, Insect Swarm everything, shrooms, maintain Sunfire since with TidyPlates you can see which ones are about to fall off.

In almost full 378s these tactics should get you to 20k easily.
Barkin - US Twisting Nether

4 set bonus is a major boost.. stupid bar.. never played a game that had such a silly thing before and proberly never will >.< read below!!