All I can suggest is find a popular celebrity on tv etc. that you like the style of, that you think will suit you. And by that I don't mean find a celeb you wished you could look like ...
Google some pictures of them, and then have a look on www.asos.com for the same styles and shapes of clothes. I'm 23, so take my advice over the rest of the old fogeys in here hahaha!
Also if you go in to some clothes stores they have stylists who can go over what they think will suit you, they'll let you try clothes on whilst you have a beer or two and they discuss different styles. The same goes with hairdressers, especially Toni & Guy will have a look at you in your new clothes to find a hairstyle that will suit you. Or you could do it the other way round, ie. find a new hairstyle and choose clothes based around that.
Also look at bands you like and see what they all wear if you like any of their styles.
And finally, the kind of girls you want in your bed.... what type of guys do they like and usually go for? Dress like them.