Fold the edge of the pants under to your desired length, and secure the fold with a pin. Iron the fold to create a crease, and cut the excess material, leaving 1/2 inch of material. Apply liquid plastic to the cut edge to prevent fraying. Using a blind hem stitch, sew the folded crease. Starting from underneath, bring the needle through the fold, and repeat until the entire fold is stitched. Tie off the end of the thread to secure.
The following tools are necessary: a needle, thread, liquid plastic, scissors and an iron. Liquid plastic, known as fray block or fray check, is available at most stores that carry sewing supplies. It dries clear and prevents the edges of the fabric from fraying.
Start stitching from underneath so the knot in the thread doesn't show. To ensure the thread does not show, use the needle to pick up a couple threads from the pants while pulling the needle through. Check the outer side of the pants before pulling the needle all the way through; if the needle is visible, the thread will be too. Simply remove the needle, and make the necessary adjustments. To add a clean finish to the newly hemmed pants, iron the crease.
Goodhousekeeping.com provides four-step instructions on how to hem pants, complete with images. The page also provides an instructional how-to video.