What connectives / conjunctions are used to correct a run on sentence?

With FANBOYS, the comma comes first, although sometimes you may not need one. It mostly depends on the meaning you're trying to convey as to what word you would choose. "I would, but I can't, so I won't." is a good example of using FANBOYS and changing or emphasizing different meanings. I hope that helps. Of course, you could just make the run on sentence into two short sentences which is sometimes very effective for emphasis.