Great point. I just reviewed one of my shorter stories that I'm preparing to submit after the Summer Lovin contest is over and found several places where I'd done this.Great thread idea.
I'll start with a simple one: "... and then..."
Pick one. Never both.
While the rules can get fuzzy sometimes, "and" works best for things that can happen simultaneously...
"He looked at her and smiled."
While "then" would confer the idea of one thing happened, then another:
"He looked at her, then smiled."
Using "Then" would require a comma.