While DMG buff CDs are definitely good to use before applying DoTs, if you have to choose one, let it be Internal Release. Assuming Straight Shot is up, thats another 10% to crit chance for DoTs, proccing Blood Letter. Additional Bloodletter is pretty much a DMG buff in itself.

But yes, buff before DoT, Stagger buffs, I personally dump all my CD's (still staggering) at once since they work with one another. Hence Quelling Strikes. Just know your fight so all Buffs arent on Cooldown when you need them most. i.e. Titan's Heart.