I have a trick that I use,I will try to explain it.......after your hair is dry,grab on side of your hair,all of it in your hand.
Have your hairspray in the other hand.Let the hair fall out of your hand a little at a time while spraying.The
spray will coat each hair strand and give it fullness.After the spray has dried.Lean your head to the
side,and spray the underneath side of your hair on both sides.Before the spray dries,spread your fingers
out and put your hands in your hair starting and your ears and hold your hair out until the spray is dry.
Then lightly spray all of your hair.Hope I explained this well enough,but it really does work.