Controlling Ascent Rate

[Air Boy]

I'm a fairly new diver, and have also become an avid one!  But the problem I keep encountering is controlling my ascent rate.  My instructor taught me that my inflator is not an elevator, nor should it be used as one.  When I don't have much air in my BC, I have trouble maintaing a steady and slow ascent rate.  On the the other hand, I have read articles that say to add air to your BC.  I think the problem here is that the air will expand as you get shallower and it will be impossible to control.  I just want some opinions/tips.  Thanks!