Thinning shears are a great tool for thinning out really thick hair and to blend layered hair better. They look like a pair of scissors, but instead of straight blades they have teeth with gaps between them. Normally, you use the thinning shears after you've already trimmed the hair to the desired length. They are tricky, so you definitely want to read some directions before you begin.
Section off the top of the man's hair once you're done trimming it. The hair can be mostly dry at this time.
Hold the hair in your left hand so it's standing straight out from the head. Grab the thinning shears in your right hand.
Cut into the hair shaft with the thinning shears. Use them just like you would scissors. They allow you to cut some hair short while keeping other strands at the original length.
Open the thinning shears to release the hair. Allow it to drop back into place. Comb away the excess hair that's cut.
Work your way through the hair. Focus on the areas that are the bulkiest and fullest. Use the thinning shears on various sections of the hair. Feel free to go back over one area for a second time if it's still too bulky.