Frankly, your best bet is to learn the medal award conditions and shoot for those, I play a pyrotech lvl 17 now, and do quite well. If theres a dedicated healer in a match I'll swap to tank mode and guard them. (1st time playing a powertech, but i've played a merc in beta and other classes so this is a learning experience for me also)
So off the top of my head for the commendations for us, 1 on 1 kill, damage awards, # of kills awards, defense award (alderaan) can net you at least 4 medals in a match and on a good match with an efficient team you can pull 8+ medals. (EDIT just saw the post above listing the medals, study that list)
DoTs are very subtle and a good dps rotation will net you good numbers and medals at the end of the match.