Ride with the flow of traffic. This is safer because the traffic coming onto the street turning right will look to the left to see if it is safe to go and will see you if you. Abide by the rules of the road. Stop at a red light or stop sign just as if you were driving a car. Wear light colored clothing or reflective gear at night.
Visibility is very important.
Ride single file when riding with friends. If you need to talk to the people riding with you, pull over and stop while talking. Drive your bike defensively. This means not to assume that cars are going to see you and stop. Pedestrians have the right of way, do not ride your bike on sidewalks.