When I was a kid there were a lot of commercials for a board game called "Thin Ice". The game was simple — one by one you piled marbles (penguins) onto a wet piece of stretched tissue paper (iceberg) until eventually the paper ripped and all the marbles fell through.
This game is exactly like the question and answer period after your presentations. When you ask for questions, nine times out of ten most people in your audience will just sit there, not saying anything, waiting for someone else to break the ice and ask the first question.
It's a fact of audience psychology. People are shy.
So why not break the ice yourself? Instead of ending your presentation with the usual "Q&A" slide, end with a slide that lists three to five example questions people might want to ask.
Example questions make your audience feel more comfortable. You're breaking the ice for them, so nobody has to worry about going first. And if you make the example questions simple, you eliminate the common audience fear of asking a "dumb question".
Pre-prepared questions also enable you to have pre-prepared answers ready, making your Q&A look more like a continuation of your main presentation, and making you look more like a rockstar.