as a dps general rule is that some of your rotation may adjust a bit, you're not aiming for heavy sustain, but high burst. dots and things do add up and can help counteract some HoT, or get kills as people run.

For drg, i'd prioritize impulse rush CD > Crit > duration. Follow with general CD's for the other abilities.
It's really a toss up what order you spend them on though, could even depend on the dynamic of your group. in frontlines you will be able to work together to chase people down or push in. fetterward/purify/and recouperate will be important for you/your party's survival. also worth knowing; purify can be used on members of your team. you can freely reset your pvp points, play around and find what works for you.

i usually point to an old thread for burst from Gryzz for drg tips/burst. the post is a bit older now but the ideas still apply. http://forum.square-enix.com/ffxiv/t...-Dragoons-Pt.2.