Engage the audience, make them part of your speech, and make eye contact, take frequent breaks during your best man speech, to emphasize the point you're trying to make. Maybe throw in some words of wisdom about your ideas, and thoughts on marriage, but be sincere and emotional. Inspirational thoughts and poems, are a good way to strengthen your feelings. If you are married yourself, then add things you have learned, and how you coped with the entire marriage process. Be sure all your comments, are heartfelt, if you're speaking from the heart, there is no way you can go wrong.