Not a big one, but one that I found helped a lot: cutting out the "filler" words ("like", "uh", "so"...). These fill words are used in many place to hold onto the listeners attention, but doing it too much can make your talk non-dynamic, and your audience will stop listening.

We have somewhat primal instincts that make us maintain focus on subtle things like body movement and differences in speech, or even lack thereof. So moving slowly from one spot to another, talking with your hands, and having _gaps_ in your speech will help your audience naturally maintain focus.

Filler words are easy to remove: just practice not saying them when you're having conversations with the clerk at the store or your friends/family. You'd be surprised how effective it is, and how much more polished you'll sound.