GETTING STARTED: THE BIKE
Just about any bicycle will work for commuting. I've

traveled to work on a mountain bike, a road bike, a hybrid, and even a fat-tired cruiser. The important thing is to get a bike you feel comfortable on. Find a reputable bike shop, consult with the sales staff, think about how you might use the bike, how far you'll be going, what you might need to carry, what conditions you'll be riding in, and so on. My present commuting bike is a cyclocross bike, which handles most everyday urban riding needs.
In much of the world -- in such countries as Japan, China or Holland -- the bicycle is valued as a utilitarian vehicle. And bikes sold in those countries come equipped with fenders, bells, lights, kickstands, racks, and, very important, chain guards.
In the North America the bicycle is generally considered a toy, a recreational device, or as exercise equipment. Something you load on top of your car, like skis or a kayak, and travel to some remote area to "play."
Don't buy a mountain bike just because there are lots of them on the sales floor or available used. Mountain bikes are fine for many things, even commuting. However, most people never get near a trail with their mountain bike. Those fat knobby tires may really dig into the dirt on a stretch of fire road. But they add lots of rolling resistance on pavement.
If you think most of your riding will be done on asphalt streets, then consider a hybrid, touring, cyclocross or a road bike. They're generally made with larger, easier rolling wheels, with street "slicks" or other tire made for riding on pavement, and offer a longer wheelbase for a more comfortable ride.
GETTING STARTED: CARRYING CAPACITY
Like any commuter, you will probably need to carry

stuff: papers, reports, tools, books, lunch, a gift for a coworker, and a change of clothing. Carrying a load while bike commuting essentially reduces down to a variation of two approaches: bike messenger style or bike tourist style.
Bike messengers are on and off their bikes constantly. They keep their bicycles light, carrying the weight on their bodies in a backpack or a cycling specific messenger bag. The advantage of this is the ease of making lots of quick stops, locking up without having to remove frame pumps, bottles, panniers, and other items. Keeping the bike light also gives you better control; you can "bunny hop" a pothole for instance, or swerve quickly amidst traffic.
Bike tourists, on the other hand, spend more time on the saddle pedaling. Carrying weight on their body would be uncomfortable over a distance of 30 or more kilometers. So bike tourists carry the weight on their bikes instead of their bodies, using front and/or rear racks and panniers (bags.) One alternative to racks and bags is a wire basket(s) permanently attached to the bike.
Most people practice both the messenger style and the tourist style. Most begin bike commuting carrying their needs in a backpack. But that often leaves shoulders sore and turns your backside into a sweaty mess. Some may buy a rear rack and attach the backpack with a bungee cord. That usually is not satisfactory, as the load falls off and moves around. Eventually most acquire genuine panniers. These tend to be stable, don't loose their load in the middle of the road, give the bike a low center of gravity and are easy to load.
PARKING, LOCKS AND SECURITY
Locking your bike is a lot like the two guys camping in the woods. It's getting late, the campfire is dying down, and one of them starts putting on running shoes. "Why are you doing that," the other one asks. "In case of bears," replies the sneaker-clad camper. "That's crazy, you can't outrun a bear," says the other. The one in running shoes replies: "I don't have to. I just have to outrun you."
The reality is that no lock is 100 percent secure. A determined "pro" will find a way to break any lock. Concentrate on making your bike more difficult to steal than the other bikes around it. "Out run the bear," so to speak. Lock it in a well-lit area with lots of pedestrian traffic.
BICYCLING SAFETY
Many beginning cyclists think that riding on the

sidewalk is safer than riding in the street. They couldn't be more wrong. Cycling on the sidewalk means you have to dodge pedestrians, pets, scaffolding, garbage cans, parking meters and signs, vehicles exiting driveways and garages, landscaping, trees and leafy debris, motorists turning off the street, pedestrians leaving buildings without expecting a high velocity traveler sharing their space, and police officers with a ticket quota to meet.
Ride in the street. It's safer and legal. Bicycling on the sidewalk also creates unnecessary enemies for bicyclists. Respect pedestrians, seniors, people with handicaps. Keep out of their space when you're on your bike.
Be assertive. You have the same right to the road as an automobile. Despite the best efforts of General Motors, the streets still allow pedestrians, bicyclists, farm equipment, horse drawn carriages, and other forms of public activity. If you don't assert your rights, you lose them. Many cyclists ride as close as possible to the parked cars on their right, frightened that an overtaking vehicle won't see them or won't wait until its safe to pass. Problem. The most frequent accident for urban bicyclists is "dooring," a collision with an open car door.
Many prospective cyclists are justifiably concerned about safety. However, the perception of danger is generally far greater than the reality. In my experience, probably 98 percent of the motorists I encounter are truly not a problem. There are some "road raging" jerk drivers out there, but for the most part, they're rare (fortunately.) You can further minimize the risk from motorists by doing a few obvious things:
1) Be Visible: wear bright clothing, ride out in the lane away from sight-blocking obstacles, and, if cycling at night, use lights and reflectors.
2) Be Predictable: maintain a steady line, so that overtaking and oncoming drivers can anticipate your course and pass safely; don't weave.
3) Communicate: use hand signals to indicate a turn; make eye contact; wave when a motorist yields to you; smile and show how much more fun you're having commuting by bike.
Again, be assertive. Take the lane! Traffic law doesn't require a cyclist to pull over every time a car approaches from the rear. You only have to be as far to the right as you consider necessary to safely operate your bike. If there's road debris, broken pavement, another cyclist or anything in the extreme right that makes you uncomfortable, move to the left. You have the right to the entire lane! Take it. You're far safer having the cars behind you than crowding you while they pass. Give yourself a cushion. Define your space. Don't be timid. Assert your rights.