Your gear may not be up to par to your level anymore, and you see that once you hit 30. Cure will always be your go to spell before you use Cure II. Also until you get more practice with DPSing and "over geared" I would suggest full healing because it is very easy to make mistakes and fall behind with healing. It's pretty difficult to clutch heal without the cool downs you will have in later levels.

When you do get comfortable enough, just assess each encounter when they happen and you can find windows to DPS if the tank isn't getting blown through like a wet paper towel.