i'm level 22 now and started off as medic. I spend most of my time dpsing. if its a group, i start with mortar and that usually kills them right off the bat. if its a tough elite with adds i have aric attack it while i kill adds. I usually find that mobs die before i actually need to heal, so i wait til its over and reload.
the only time i ever focus on healing is in flashpoints because i need to conserve ammo to heal instead of dps.