1. Follow "fashion" less and personal style more. Style is what makes you an individual and it's WHO you are that makes you attractive to other people. Following "fashion" simply makes you one of the herd and one-dimensional. It doesn't matter if your style is boho, conservative, clean cut, or way, way casual. Whatever it is, own it and know yourself.
2. Remember that your style is what you are actively saying to other people. How you present yourself to others matters, no matter how many times you hear "it's what's on the inside that counts." That may be true (I certainly believe so), but who you are on the outside also gets a say, especially to people you aren't familiar with.
3. Dress appropriately for the occasion. No jeans at a wedding and no shorts in the middle of winter. And please, no black socks at the beach (European guys: index and middle fingers pointed at my eyes, now pointed at you).
4. On the subject of socks, most guys have WAY too many pairs of white tube socks. You need 2 pair. Get rid of the rest and invest in some black, brown, beige, and, if you can rock it, red socks. Never wear white socks with sandals/flip flops unless you are in a traditional Japanese kimono.
5. White jeans can be worn, but not with white shoes, not on a cold day, not on a rainy day, and not with colored underwear. And for the sake of baby Jesus, never go commando with white jeans/pants.
6. Matching is a basic element of style. Sophisticated men know when to match and when not to. Every man should know that matching everything makes you look like a pimp. In general, belts should match shoes and ties should match pocketsquares. However, rules are made to be broken - just do so consciously. Stripes on stripes is only for experts, and even then I'm not 100% sold. To see men who are breaking such rules, with varying levels of success, check out the book "Gentlemen of Bacongo":