Always wear a helmet.
Learn, use, and obey traffic signals. Remember bikers must obey the same traffic laws as motor vehicles.
If riding at night, use reflectors and lights.
Give pedestrians the right of way.
Ride defensively. Watch for cars and car doors opening.
Do not weave in and out of traffic.
Slow down at intersections. Look both ways before crossing.
Keep your bike well maintained. A regular tune up will ensure that your bike is in good riding shape.
When you are not riding your bike, always lock it.
When riding at night, make sure to wear reflective clothing and have reflectors on your bike. A light on your bike is also highly recomended.
A Guide to commuting on a bicycle (.pdf document)