I have found that the best way that an instructor can help with retention is to try and spot a problem with a student in the early stages and direct them to the appropriate personnel to deal with what ever might be going on in the personal or life at school.

I have found that the best way to motivate a student is, to come in with a sense of excitment. If you are excited about what you information you are conveying then the student will see that and then it becomes easier for them to take a intrest in the course, for the simple reason that they see how enthused you are about teaching it.