Watch a sign language video that teaches the ABCs. View it a few times to get a basic understanding of how the hand movements work and how each letter looks. Once you have a basic understanding of the ASL alphabet, watch the video a few times at a slower pace.
Form each letter as it is displayed in the video. Pause the video, if necessary, to take the time to form the letter correctly. Realize that it may take you several attempts to get the formation perfect.
Quiz yourself by trying to form each letter of the alphabet before it is displayed on the screen. Keep a list of letters you struggle with so you can spend extra time practicing them.
Practice your letters in the mirror each day. Watch your hand placement and formation to make sure you are forming each letter correctly.
Spell words using ASL each day. You can do this alone or with a friend. If you sit in a chair, try to spell "chair" using the sign language alphabet. When you cook spaghetti, try to spell that word. Look for opportunities in your daily life to practice your spelling and review your letters.