I really like this video done by the city of Chicago. They clearly and eloquently explain why we should ride in the middle of the road with our cycles and stay off the sidewalk. In fact, it's the law that nobody over the age of 12 can ride on the sidewalks.
What's the big deal? Aren't sidewalks safer? Truth is sidewalks can be dangerous and a pain. It's not fun avoiding overgrown trees and navigating narrow walkways often with people on them. Pedestrians can be very unpredictable. If you are going to bike on the sidewalk (even illegally) at least do it in the direction of traffic. That way cars can be somewhat on the look out for you when they are making turns.
America does not have safe cycle paths like the Netherlands. Instead we encourage cyclists to "take the road". Be sure you take a whole lane when you bike. Don't try to ride on the side of a lane to be "nice" and let cars pass. Hog the whole lane yourself with your bike right in the middle. Don't give a motorist the chance to hit you with their side mirror or worse. It is dangerous to share the road with cars but it is more dangerous to ride on the sidewalk.
Until America makes safe cycle paths be brave and take the road. It's the best option and more fun too.