Find a Good Spot
Make sure you know the airshow's schedule--some schedule aerobatic shows throughout the day, while others feature mostly static displays and ground events, but end with a single aerobatic show. Before the show you want to see, stake out a good spot.
What's good? Generally, the more centrally you can position yourself along the viewing area, the better. That's where the announcer booth is located, and where the aircraft will tend to do their most interesting stuff. It’s also where the biggest crowd will form, so you might need to pick a spot early.