dps is average damage done per second over X duration (entire instance, just trash, just a boss etc... if you use the dps figures you get for a boss fight they're likely to be more accurate to what you can do than the figures over the entire instance.. which'll take into account time spent idling)
overall damage is well... dps * time spent in combat * efficiency rating of using said time
the efficiency rating is there because nobody can use 100% of the time spent in combat purely for dpsing, but they can get close. the highier your efficiency rating the closer you'll get to maximising your damage done
now to up your dps... firstly try not to waste time moving; getting into place; canceling spells etc.. all these types of interuptions lower your dps.
2ndly. keeping a VERY tight dot rotation is para-mount. as I presume you're a UA lock, keeping UA, Cor and immolate up is necessary (don't worry about siphon life, and seeing as you're on CoE duty you should have no issues with that, 5minutes is plenty of time to not care ^^). to improve your dot uptime, don't wait for UA or immolate to run out before recasting them, when they get to 2-1.5 seconds to the end of their dot cycle, start recasting them.. BUT (and this is a big BUT) NEVER cancel casting SB to start re-dotting. if you've started a spell, finish it. also if you've just finished casting SB and you're at 3-2.5 seconds to the end of the dots... DON'T wait. cast a SB, and then redot. wasted time = wasted DPS (though if your mana is getting low, or you think you need to reposition yourself or something.. lifetap/darkpact/move instead.. the time isn't being wasted this way either)
umm.. otherwise... get more +hit if you're not capped, get more +dmg/+shadow and the main law of good dps. DON'T WASTE TIME
I hope this helps :)