Summarize:

Grab a partner. Place your throwing arm in the air at a 90-degree angle, but support it at the elbow with the glove on your other hand. Using just your wrist, toss the ball to the other person. Sit with your legs outward. Start with your arm in the air at a 90-degree angle, supported by the glove on your other hand.  Start by using just your arm from the elbow up to throw the ball.  Move on to twisting your whole torso while throwing, as well as your hips.  Next, move up to one knee and practice twisting and throwing from that position. Try to throw across your knee (angle-wise).  Finally, stand up, and keep focusing on following throw by twisting your torso. You can also add a crow hop, where you jump forward on your forward foot as you wind up. Outside of practice, you should be practicing throwing three times a week. You'll need to spend about 15-20 minutes throwing each time you practice, throwing at various distances.  If your age is 7- to 12-years-old, spend four minutes on each of the following distances: 30 feet, 60 feet, and 90 feet.  If you are 13- to 20-years-old, spend four minutes on each of the following distances: 30 feet, 60 feet, 90 feet, and 120 feet.  Try to throw straight across the field instead of making them arc high. Don't throw with all your force, but you want to make a good line from where you are to who you're throwing to. This exercise works particularly well for little league players because it works the arm, as well as the rest of the body, but it can just be a fun activity to do with a friend or a parent. Simply get an appropriately sized football, such as a junior football for little leaguers, and grab a partner.  Put the emphasis on targeting the ball. Make sure the ball is going into your partner's chest. Throw at least 15 to 20 times each time you choose this exercise.
Work on the wrist throw. Work on throwing in different positions. Practice long throws three times a week. Try throwing a football around.