Personally, I think guys are hottest in well fitting jeans and a well fitting tshirt, but if you're trying to look a little nicer, try a button down with the sleeves rolled up. Oh, and nothings worse than when a guy looks nice and I look down and his shoes are jacked.
And lol @ Hurricane mentioning Hollister & Abercrombie. Hollister is meant for 14-18yo and A&F for 18-22yo. They're 22-35yo brand, Reuhl, closed last year so don't bother. Regardless, I really dislike any of these brands on guys. Don't do it.