There are shelves and shelves of shampoos, solutions, conditioners and concealers that promise to thicken up thin hair. On the opposite end of the spectrum, little attention is paid to the gals and guys who wish to make their thick hair a little finer and more manageable. Going from thick to fine is totally possible, but first you have to choose whether you just want a lighter look or if you're actually willing to lose some locks.
Leave a bit of conditioner in your hair rather than rinsing it out completely -- give your hair a quick rinse of cool water instead of a long drenching under a hot shower. This keeps your hair from getting too puffy, creating a thinner, finer look.
Apply a straightening balm to your hair before you blow-dry, especially if your thick hair is also coiled or prone to tangles.
Ask your stylist to give your hair thinned-out layers with thinning shears or a straight razor. This technique gently removes the top layers of your hair, leading to less thickness, increased manageability and a finer texture. It also helps reduce frizz and puffiness, common issues for those with thicker hair.
Request a haircut from your stylist that takes weight and thickness out of your do, such as loose waves with bangs for medium-length hair. For long, straight hair, go with long bangs and long hair around the crown, with plenty of texture in the last 4 or 5 inches of hair -- this will give your hair a little lift while reducing the thick, puffy look. If you're willing to go short, choose a graduated bob for a light, fine look.