The right gel, haircut, and plopping all will you get more volume, but to a certain extent there's not a whole lot you can do. My hair is really flat on top; the only way to get more volume is to cut my hair until it's at least shoulder length. This means sacrificing my current length, which is "bra strap" length, and returning to the dreaded "pyramid head".

This doesn't sound optimistic, but I have learned to like and appreciate my hair in its current...state, for lack of a better word. An actual useful tip that I will pass on is this: After diffusing, I usually pin my hair up with several butterfly/claw clips, creating an updo that lifts the hair at my roots. If I wear my hair up all day, it can "set", and when I take it down at night it has the perfect amount of lift that I need.