Fashion is very subjective but generally speaking tighter fitting clothes are better than baggy clothes. Figure out if you have warm or cool skin tones and stick to those colors (the easiest way to test this if silver or gold looks better on your skin, if silver go cool colors, if gold go warm). High contrast between your bottom and top half is risky. Generally don't wear only muted colors (white, black, grey, brown), some flare is important. You don't want too much of a pattern and do not mix patterns. Accessories can help a lot. Matching colors are cool but don't overdo it. Layering with jackets/sweaters is very cool too.

If you're muscular up top you can get away with breaking these rules somewhat.