Specific topics will allow you to focus your comments on the points and bring real insight to the audience. The use of gestures is a learned skill. It will become more comfortable with time. In everyday conversation, we use gestures naturally. As you master conversational quality, your gestures will follow.
Some people like to plan gestures to use at specific times throughout the speech.
I do not recommend this practice. The question of too much gesturing came up several times. I do believe that you can over-do it with gestures. I would say that when the gestures begin to distract the audiences attention from the speech, you have gone too far. Gesture over-load occurs most often when we attempt to artificially plan gestures to insert in the speech.