What to Wear
Always wear a helmet---this is the most important piece of safety equipment while riding your bike.
If your bike has quick-release wheels, make sure the levers are tight. Check tires for proper inflation---the correct pressure can be found on the tire's sidewall.
Riding at Night
Wear bright clothing, fluorescent if possible. Use a flashing white light in front and a red one in back. Many city ordinances require the use of a light at either the back or front of the bike, or both.
Laws for bicycles vary by state (and sometimes by county and city). Most states apply the same laws to bicycles and automobiles. Most states also require children to use a helmet, but the age varies by state. Many city ordinances require the use of a light at either the back or front of the bike, or both. Many states also have laws against riding with both, or even just one, ear blocked by earphones.
When riding in traffic, try to leave a little cushion of space between your bike and parked cars, as this might give you extra time to react if a door suddenly opens in front of you. Use hand turn signals where necessary. Always be aware.