- Use a good lock. Thin cable locks are fine if your bike is in your plain view, but U-locks are the only good deterrant.
- Don't keep the bike on the front porch. I've known several people who've had their bikes stolen from the front porch, even when the bike is locked to something.
- Don't hide the bike. Don't park your bike back by the garbage dumpster or behind a wall; that allows the thief to work without observation. Put the bike out front where there are people.
- Don't just lock the front wheel. To me it's unbelievable that people do this, but I see it all the time. I also see a lone wheel without the bike locked to a bike rack all the time.
Photo info: NL/Nieuwegein/Bicycle? by Oop.