I only have ARC at 15 so I could get BLM unlocked (really need to go back and get quelling strikes... >_>), but from what I understand ARC/BRD has no 'rotation' really, just a series of priorities like urth said -- keeping DoTs active and taking advantage of procs as they happen. Early on this probably doesn't amount to much, just like with other DPS jobs your rotation at level 8 is 2-3 abilites over and over.