biggest mistake i think people start doing is over editing. not EVERYTHING has to happen with the beat of the song. Sometimes simple is much better.
Don't leave black video gaps in your edit.
Colors. White balance always. You can always play around with colors in post it's best to keep them fairly neutral while shooting.
learn what your export settings should be depending on what your exporting for. if your uploading to web learn what deinterlacing is.
Never ever use gay cube effects or any other effect that any one else can use with a click of a button (besides basic fades and such). It just shows your amateur.
Try to be creative, listen to a song and picture it in your head and get the shots you need to make it happen.
I don't know those are just things i thought id say.