In my honest opinion, there can be no set rotation for any class as the encounters in this game call for adaptation. There are, however, things you should be doing in each fight, granted it lasts long enough.

Ideally you'll open with Fracture and Phlebotomize followed by your Chaos Thrust combo to apply all your DoTs. Then you can start opening up the Can 'o Whoop-Ass while weaving in Feint, Jumps, stuns, and buffs to your hardest hitting attacks until you need to reapply your DoTs.

This is really all you need to know as a Dragoon in order to maximize your party effectiveness. It isn't exactly rocket science. Trying to stick to a set rotation in this game will always hurt more than help.