The most fabulous collection of bike commuting tips are here. I could not possibly come up with anything as comprehensive as this.
But I want to add my own tips too, just because I can. The first is some encouragement - yes you CAN ride your bike to work. It isn't the most frugal means of transport, which is walking, but it is way better than anything else around. Anybody who travels 5 miles or less to work can easily bike. 5-10 miles is harder but still doable for the novice. 10+ miles is getting daunting, I admit, but you can work up to it. This recent article in the New York Times talks of one guy who commutes 40 miles by bike. Um, yeah. It might take me a while to work up to that, but hey, you never know. Also, if you live far away, don't necessarily think you have to cycle the whole distance - maybe you cycle to a bus stop, take the bus, and then cycle from that bus stop to your work or school. Buses around here have bike racks on their fronts that are easy and quick to use - even if you have to ask the driver to come out and show you how to operate it the first time, as I did.
As for safety, just be alert, don't be afraid to wear dorky things like helmets and reflective gear, and follow the road rules. Signal with your hand if you are turning. Pay attention. There are risks, but you can minimize them by choosing your route carefully and being alert. And, 24% of bike fatalities involve an intoxicated cyclist, so that's definitely something that can and should be avoided. The failure to wear lights at night or a helmet significantly increases a biker’s risk. Finally, newer riders have to be especially careful about drivers opening doors (you’ll get clipped) and making turns (they can’t always see you), and about riding on the sidewalks (you’ll get hit by cars exiting or entering driveways). See here for some of the safety information.
So:
*Start with one day a week. Fridays are good. You might want to do a few practice runs at the weekend to build up to the mileage you'll need to do.
*Get a helmet. This is an absolute must.
*Get mud flaps/fenders. You will at some point have to either cycle in the rain or go out on rain-splashed streets. You do NOT want this up your bum.
*Get lights. Seriously. No lights, no riding. Even if you don't plan to ever ride in the dark, you just never know when you're going to get delayed at work or if you're going to have to ride home while a storm is brewing.
*Get a bell or horn. This is another seriously. I tried to do without for a while, but I got shouted at several times for not alerting pedestrians to my presence. Pedestrians (especially, I have to say, older women with small dogs) get angry if you don't give them a wide berth as you are going past them.
*Get some reflective/flashing stuff for your bag or person. I like these which can fit on a bag strap. Sing along with me: I'm a dork, and I don't care.
*If your workplace doesn't have showers, take some wet wipes (or a damp wash cloth in a plastic baggie) and fresh deodorant, and wipe yourself down when you get there. Don't try cycling in your work clothes unless you are doing a mile or less. Change when you get there. Equally I'm not too keen on tight spandex that you'd be embarrassed to be seen walking in to the office building in, but whatever floats your boat.
*Use the balls of your feet on the pedals. I want to shout at everyone I see using their arches/middle of the feet on the pedals - you get much more bang for your buck with the balls of your feet as you can get more power.
*Think about changing your route or your hours to accommodate biking. It is much more pleasant cycling to work in the summer if you go earlier in the day when the sun hasn't had as much of a chance to heat the air up. Likewise in the winter you might want to go a bit later in the day. Cycling is also more pleasant if you are on smaller roads - if you normally drive along a busy highway, think about the smaller side streets that run parallel to the highway. Check google maps or mapmyrun.com for a route. I was able to cut half a mile off a 4.8 mile commute just by carefully selecting streets based on the distances that mapmyrun was showing me.
*Think about changing your route or your hours to accommodate biking. It is much more pleasant cycling to work in the summer if you go earlier in the day when the sun hasn't had as much of a chance to heat the air up. Likewise in the winter you might want to go a bit later in the day. Cycling is also more pleasant if you are on smaller roads - if you normally drive along a busy highway, think about the smaller side streets that run parallel to the highway. Check google maps or mapmyrun.com for a route. I was able to cut half a mile off a 4.8 mile commute just by carefully selecting streets based on the distances that mapmyrun was showing me.