I have fine 3c/4a hair. Using a volumnizing product to wash usually helps. For example Herbal Essences Body Envy to co-wash. Then, using a light protein/moisturizing leave-in (ex. Mane n Tail Detangler) and sealing with Castor Oil, which helps your hair appear thicker and over time does thicken your hair. Sometimes, I mix my leave-in with a bit of PM Skinny Serunm so that my hair dries quicker and is bouncy but I use very little of it. Since i'm air drying, keeping it simple and not being heavy handed with product application is the key to full, bouncy hair.
After putting in my products, I pin up my hair until it's 80% dry, then I let the rest of my hair dry loose. Letting your hair air dry outside in the breeze also helps.