If you’re presenting from a lectern, don’t grasp the sides of the lectern like a drowning sailor clinging to a piece of driftwood. Your white knuckles will show and you’ll only become more tense.
Instead, rest one hand atop your notes (if any) or in the center of the lectern top and use your other hand to gesture. This position not only will look more natural and effective, but it will be more relaxing, as well. As your presentation goes on, bring up both hands to gesture occasionally to reinforce a key point.
Remember to turn your entire body–not just your head–toward various segments of the audience. When you turn to your right, rest your left hand on the lectern and gesture with your right; turning to your left, it’s vice versa.