How does one become knowledgeable about fashion?

I'm a guy who formerly had absolutely no sense of fashion or style. Clothes were just something you put on to keep warm. However, with some coaxing from my girlfriend, I started buying some "brand name" clothes and I started really enjoying the way I was looking. Since then, I've gotten an interest in fashion and looking good, but I don't have a clue where to start. How do you go about figuring out what suits you and what's in fashion? I want to learn to develop my own style eventually, but I also wanna learn to understand fashions and trends. Any suggestions?