Find good role models and steal their ideas. Adapt or adopt some of the elements of their style and make them your own. When you hear truly excellent speakers, look and listen closely to understand why they make such a strong impression.
Listen to their pacing. How much do they use silence or pausing? How long is each pause? One second or less?
Watch their eyes. Are they looking at their notes, or making good eye contact with listeners?
Look at their gestures. Could you adapt a particularly effective gesture and make it your own? Expanding your gestural vocabulary is like expanding your verbal vocabulary; just as you can learn a new word and use it tellingly, experiment with learning a new gesture and make it part of your personal style.
When you hear mediocre speakers, ask yourself why they make a poor impression. Count the thinking noises. Observe how they move. Are they pacing as they speak, or fiddling with a pen? Note those elements of style that you want to avoid in your own delivery, and practice doing the opposite.
Pay attention to the people you hear and see speaking every day. Watch your colleagues and peers or to people being interviewed on the news. If you want to take it a step further, observe fellow attorneys in action in the courtroom. One excellent source for this is the United States Court of Appeals for the Ninth Circuit – they have their own YouTube channel where you can stream proceedings live or watch videos of earlier proceedings.
What do you see and hear, from the lectern and the bench?