This is an article published by the National Council of Teachers of Mathematics offering tips for tutors. Most of these could also be applied when creating videos to post online for students to use as well.
This website has a large bank of resources for teachers. The videos and resources that I previewed seem to try to incorporate a variety of learning styles and thinking skills. Most of this site focuses on lessons and resources for teachers, but these could be alternative methods for re-teaching or tutoring students as well.