I don't have much to add since the rules you're supposed to follow have already been covered. What part of MA are you in? We have some crazy traffic here but it is definitely possible to ride on the majority of the roads. One thing that wasn't mentioned yet (and doesn't really have to do with the rules of the road but is a good idea) is making sure you are highly visible when you're riding. Wear a really bright top, or a fluorescent reflective vest. People aren't necessarily expecting to see cyclists, so we need to stand out.