I would also like to point out that I wouldn't use "better", I would say "You look great" or something similar. If you say "better", you're clearly comparing it to some previous (unstated) time.
If I say to someone "You look better", it's normally because they've recently been ill (sick) and hadn't looked healthy the last time I saw them. If they've recovered by the time I next see them, then I would say "You look [much] better".
- For Teachers