Adjust your saddle if necessary. There have been some articles recently on how important saddle adjustment can be for comfort and to avoid pressure in the wrong places. A helmet, of course. The helmet is the most important, yes. Make sure it is well adjusted, fits level, and won't slip around too much.
Bike shoes are good because they have rigid soles and spread the pedal pressure evenly.
More of your energy gets to the pedal. Running shoes are fine for shorter rides. The top that you wear should have a close-fitting neckline. If you have children, review the basic safety rules with them while you are checking over their bike. So we're all set to go.