From looking through GQ, I wouldn't recommend it. Their fashion advice is expensive, time-consuming, and too oriented on details that most people wouldn't notice. Women have tons of great magazines with various degrees of fashion advice, but I haven't seen a good one yet for guys. However, Queer Eye for the Straight Guy on TV usually has some really good, simple tips for guys that aren't too difficult or expensive to adapt into a typical guy's routine. They're really good at creating a manly makeover that a guy can actually stick to and not be embarrassed about.
For hair, find a stylist that comes up with a look that you like that's easy to do and takes less than 5 minutes every morning. Then, stick with her! A slightly different cut and a teeny amount of hair gel might make a huge difference. Try a few stylists out and get your lady friend's opinion on each cut, then stick with the one who does something you like. Keep an open mind; it's their job to know whether a middle part looks good on you or not.
And remember, a haircut doesn't cost $5. Be willing to spend at least $20, and don't complain about it -- girls can get stuck with cuts in the $60 range!
You might also want to ask the stylist or your friend what they think about your sideburns. Depending on what shape your face is, slightly longer (or shorter) ones might look really awesome on you. Sideburns are one of those things you can change without venturing into the realm of facial hair, if you have strong feelings about it.
For fashion, like I said, don't bother with magazines like GQ. If possible, get honest advice from a male friend you consider to be well-dressed. If you don't have any friends like that, go to a place that's full of well-dressed guys your age (whether it's a classy nightclub or a certain shopping district) and try and discern fashion patterns from the crowd.
You could also have a lady friend take you shopping. One thing that a lot of guys don't know how to do is find a flattering color, and girls are great at recommendations in that department. My brother looks hella awesome in baby blue, for example, but he always wore black until his girlfriend got him a blue shirt that she just loved on him. If you find a salesperson at a store that seems pretty cool, they can also suggest stuff for you.
Trying tons of stuff on isn't exactly necessary, but it helps. Especially if you have a friend or salesperson recommend stuff for you -- just get used to the idea of trying stuff on!
And again, a flattering pair of pants doesn't cost $15. Definitely find something that you can wash at home, but remember that a good pair of pants or a nice shirt can last you years, so you might as well invest a bit in it.