Watch for cars pulling out. Make eye contact with drivers. Assume they don't see you until you are sure they do. Scan the road behind. Learn to look back over your shoulder without losing your balance or swerving left.
Some riders use rear-view mirrors.
Avoid road hazards. Watch for sewer grates, slippery manhole covers, oily spots, gravel, ice. Cross railroad tracks carefully at right angles. Keep both hands ready to brake. You may not stop in time if you brake one-handed.