To me, there are 3 musts if you want to look good:
1. Clean, well groomed/styled hair.
2. Clear skin. I know some people can't help having blemishes, but clear skin makes a person look so much cleaner.
3. Moderate make-up.
In addition, if you want to be eye-catching, you can dress to show off
ONE part of your body. Be it either your legs, your cleavage, or your shoulders.
But you don't even have to show skin to attract attention, if you wear the right combination of clothes, it's good enough.