I guess I should get around to writing some tips, huh?
Here goes:
1. Don't put a single comma between a subject and its verb. For example, "The man who went to the store, bought some bread." It was once common practice to do this when the subject had some sort of complement (like "who went to the store"), but it has long since been abandoned.
2. Check to see if your single comma really should be double. "The man, whose name was Fred went to the store" is incorrect. Use a pair of commas to set off parenthetical clauses or phrases. If you'd use two parentheses, you should use two commas.
3. If you're unsure what to do, take a minimalist approach. Don't try to use things like semicolons, dashes, or ellipses if you're not comfortable with them. All of those things can be replaced with commas or periods without any great loss.