Leave your fear of looking foolish at the door so you can spend more time generating ideas and less time worrying what people will think of you. Risk looking foolish. Not all ideas are going to be mind-blowing. Or even good. The path to good ideas means you’ll need to suggest, and remove, the bad ones quickly and without fear or judgement. Be willing to share the bad ideas.
Lead by example. If you’re willing to look foolish it levels the playing field and lets everyone know they can speak their minds without fear of judgement. Have you ever been to a party where everyone is polite and restrained? It's pleasant until one person arrives who is so comfortable in their own skin that it gives everyone else permission to relax and have more fun. Be that person. You don't need to be a extrovert and you don't need to be over-the-top to set this example. Just be engaged and willing to challenges people's expectations.
Have some fun, for crying out loud, and don't take yourself so seriously.