When in doubt, ride like a car. Allow cars to pass on your left as long as there's room and it doesn't endanger you, but when it's necessary take the entire lane. If you're riding a lot slower than the other traffic you have to be careful, check your back, start moving out and give clear hand signals well in advance, but when you have to change lanes you have to. Make sure you're visible and DO IT.

If traffic is heavy, fast or it just feels too dangerous, stay on the right until you find another way to cross. Just like when you were a novice driver, you can't win'em all