Repeat after me: I am a Car. I am a Car.
Learn and obey traffic laws peculiar to the jurisdictions around your home and work place. Bicycles are generally regarded as vehicles, and cyclists have the same rights and responsibilities as motorists in most states. However, some traffic laws apply particularly to bicycles, and they should be obeyed when applicable. Ride with traffic, predictably and following the rules of traffic flow. Riders who do get to their destination more quickly, and about five times more safely, according to scientific accident studies, than riders who make up their own rules.
Assume a lawful and predictable position in the roadway. At intersections, move to the correct lane position depending on which way you'll be going. Often you'll need to move away from your normal position near the right of the road. If you're turning right, keep to the right, and if you're turning to the left, move to the center of the road. If you're going straight, go between the right- and left-turning traffic. Meanwhile, signal your intention to other road users with your left hand, scan the roadway behind you, and yield to overtaking traffic.
Assume the Position
When the road is wide enough to allow a car to pass comfortably in the midst of oncoming traffic, try to ride as close to the right side of the road as is safe and clear of debris. The only exception is when you deem the rightmost lane too narrow to share with cars. In this case, take it over by riding on left tire track location for cars within that lane.
I used to follow Forester's theory of riding in the centre or to the right third of the lane. However, as soon as traffic gets dense enough for cars to travel in groups of three or more, drivers frequently honk and graze your handlebars. By being to left third of the lane all motorists seem to understand that you are in possession of the lane within one's legal rights.
Be Afraid. Be Very Afraid.
Remain alert at all times and watch the road ahead for any special hazards that can cause a bike to fall. Beware of any slippery or loose surface: gravel, snow, ice, leaves, oil patches, wet manhole covers, and crosswalk markings. Be especially careful when crossing diagonal railroad or trolley tracks, curb lips, steel-grid bridge decks, cracks in the road, and large bumps or potholes. Avoid them or ride over or around them slowly. Don't suddenly turn, brake, or accelerate. Be ready to put a foot down for balance.
Braking
Learn how to use your brakes and stop safely before riding your bike in traffic and on slippery pavement. No matter how cautious you are, there is always the potential for a sudden stop -- to avoid an unexpected maneuver by another road or trail user, to avoid a storm grate, or to prevent any other unexpected incident or obstacle. In order to stop safely your brakes must work powerfully and smoothly, and you need to know how to apply them properly.
The best method for a fast, safe stop on dry pavement is to use both brakes in a three-to-one ratio. In other words, apply three times as much pressure to the front brake as you would apply to the rear brake. Practice braking in this manner while riding slowly in an empty parking lot. You will notice that when you stop, most of your weight transfers to the front wheel of the bike. To compensate a bit, try to shift your weight back to keep the rear wheel from lifting off the ground.
On slippery pavement, reduce your speed and apply your rear brake lightly to avoid a skid. When riding in the rain wipe the wheel rims dry by slightly applying the brakes in advance, well before you need to stop. Read more about braking technique.
Darkness
Cycling in darkness requires special techniques. Choose the route that offers a reasonable amount of ambient light and activity. Keep your speed within the limitations of your lights. When sharing the road with cars, watch your shadow produced by cars approaching from the rear. If the shadow moves to the right, the car is passing on your left. If it just shrinks without shifting to the side, then some redneck in a puppy-crusher is about to try to graze you, so get off the road quickly and let the car pass. Be sure to install a rear LED blinker if you ride after dusk; it helps drivers to think of you as something other than road debris.
Read all about riding at night, and see the current Moon phase while you're at it.
Escaping Traffic?
Be especially careful when riding on a bike path or sidewalk. Sometimes a bike path may provide a pleasant alternative to a crowded street or highway; but they are much more likely to send a rider to the hospital. Bike paths are not designed for high speed bike traffic, and they can get crowded with roller skaters, dog walkers, careless and inexperienced bicyclists, and unpredictable pedestrians. Never pass another trail user unless you have his or her attention. Signal with a bell, a horn, or shout a friendly greeting when approaching a pedestrian from behind, and signal with your left hand when making other maneuvers. Keep your speed down so that you can stop suddenly in any situation.
There's tons of great traffic riding tips to check out in our Bicycle Safety section.
3 comments posted so far.
That all said, it's always better to be safe than right. If the road is dangerous to ride, then the "long" route may be better. Another 10 minutes of your day is probably better than risking your life.
Motorists will often become upset when they see you riding outside the bike lane, but remind yourself that these are the same ignorant motorists who open their car door without looking back.