I was taught by a top pitching coach and believe the following method to be very effective.
Release your glove hand and your other by letting them fly out (one going towards second and one going towards home). This should take on an almost flapping motion as they fly out similar to you spreading your arms like they were wings.
Then, as your continue your motion towards home, you will start to bring your lead arm forward and at the same time turn your glove hand back in and drive it towards its arm's arm pit. This glove hand should feel similar to if you are cradling a football under your armpit.
Finish the pitch by throwing over your lead leg.
These three steps will give you added strength in your motion. You want to bring the glove arm back in because it will give you more power and momentum in your delivery home.
Baseball Pitching Tips