LOL, "WE DO NOT WRITE IN SECOND PERSON!"
I forgot about the -ly adverbs though, that's another big one. Really though, the first word that jumps to mind when you're writing is more likely than not going to be an overused one you've seen used in a similar way a million times before. Vague or extremely casual language is best avoided. (In narration. You might need to do the opposite to have realistic dialogue...)
Don't go overboard with the flashy alternatives though. The goal when writing is always to communicate a thought or image or action across to the reader as clearly as you're able, so in some cases it could be counterproductive tying a sentence in a knot trying to avoid the most obvious word or phrasing for a situation.