You can't make people smarter. You can expose them to information, but your responsibility stops there. - Mark Rippetoe
Pull-Up Instructional VideosEdit
You'll need Adobe Flash installed to view the videos on this page.
Free Download Here.
Here are some possible variations that you could incorporate.
(NOTE: He is not getting full range of motion on these, you should be going down until arms are fully extended.)
If you aren't strong enough to do a bodyweight pull-up, try some (or all) of these ideas:
Band assisted pull-ups: