A good volumizing shampoo, first of all. I like Biolage Volumizing Shampoo, but find one that works for you. Next, dry your hair upside down until it's nearly dry. THEN apply a volumizing mousse, and finish drying your hair upside down. When it is dry, turn your hair dryer to the "cool" setting and stay upside down until your hair is completely cool. Then you can finish your style as usual. There are also "root volumizing" sprays available on the market which you might try, but I've yet to find one that doesn't leave my hair feeling dirty or sticky.