[mod]I'm gonna move this over to Resource Support.[/mod]Making a particular study of folds helped me a lot. There's a lot to consider from the thickness of the cloth to how stiff it is, to how loose it is on the body, where the fabric would pull and where it would hang and so on. If you mean clothes design, then considering the life of the character and what situation they're in when they wear the clothes is really helpful. The clothes tell you quite a bit about a person and it's part of the storytelling process.
What sort of tips in particular are you looking for?