Plenty of people-including us-will gladly tell you to get out of your car, and get on a bike: You'll winnow your carbon footprint to a baby step; you'll get outside and get a workout in the bargain. So let's say you do. What now? A street full of whizzing cars isn't the cul de sac where you first rode without training wheels. You can't ride with the same carefree attitude.As a bike commuter in New York for nearly a decade, scrapes have taught me a lot. I've ended up on the trunks and hoods of cars and ridden straight into their sides. I've gone over my handlebars, at speed, twice-one time landed me in the ER, the other split my helmet neatly in half. It was my fault every time. Not that I was asking for trouble. But I could have prevented these accidents with foresight. With experience, I no longer ride like I used to. Here's what I've learned:1. Even if you can't see trouble, you can sense it by attending to your surroundings. Upcoming intersections are a major source of accidents but many people roll into them blind, hoping to react to whatever might come. A better way: Use walkers as a clue to what's going on ahead. Are they crossing in your direction? And more importantly, have people suddenly stopped? It sounds obvious, but most bike riders pay attention only to the pavement in front of them. That's a good way to get hurt. Also, if a car ahead of you swerves right, there's a good chance they're trying to pull a sudden u-turn. Slow down in response.2. Learn how to turn your head correctly. Most bikes, especially road bikes, make you hunch over at least a little bit. That means you can't look over your shoulder as you normally would when walking, by keeping your neck straight and turning your head. If you do that on a bike, you're blinding yourself to the road ahead and you'll naturally turn your shoulders too. That throws your balance off and makes you more likely to fall if something unexpected happens in front of you. Instead, if you're looking left for example, lower your chin onto your left collarbone. You won't have to turn your head from the road, and you won't shift your center of gravity.3. Drivers will drive wherever they're given room. So when you're sharing the road, don't encourage them to squeeze past you. Claim your space, especially on busy streets. Don't hug the curb to give yourself a slim profile. That only encourages drivers to whip around you. Instead, give yourself a wide berth. The worst you'll hear are honks. The alternative is getting knocked off your bike while trying to be polite to a driver who doesn't care.4. Look at the road from the standpoint of the cars around you. Be aware of where drivers' blind spots are. If you're in one, slow down or speed up to get out of it. Never, under any circumstances, put yourself between a big truck and a curb. Too many people get seriously injured or killed when trucks swerve or turn suddenly. You might feel goofy stopping behind a truck at a light and not passing it when there's a three-foot gap on the side. Deal with it. Be patient.5. Don't ride fast at night. Accidents happen faster when it's dark, since you're slower to react when you can't see as much. And an unappreciated danger is the road itself. If you're moving quickly, a small, invisible bump can send you flying. (This is what produced my most potentially severe accident, when I cracked my helmet.)6. Most wheel and bike thefts take just a few seconds. Increase the time required to steal yours. A couple of tips:-Don't skimp on the lock, and lock your bike right. Those ubiquitous black-vinyl covered U-locks are terrible-they can be popped with a six-inch piece of metal. Cable locks are just as bad. Get yourself a hardened u-lock, or, better yet, a city chain like the messengers use. They're not heavy when worn around your waist. When you lock your bike, loop through the wheel and, more importantly, the frame-few thieves will saw through it to steal your bike.-Your bike wheels probably come with quick-release skewers, the bolt that attaches the wheel to the front fork or rear wheel stays. Tell the bike store to replace them with regular bolts that require a wrench. That'll make your wheels slow and annoying to steal, and wheels are surprisingly expensive to replace.-Sounds dastardly, but if I'm parking my bike next to a bunch of others, I'll do it close to a bike that's obviously easy to steal, leaving any bike thief to wonder: Why steal this one when that one is easy pickings?7. Wear a helmet. If you're too embarrassed, you're also too dumb to ride a bike in a city. Seriously.