Most guys aren't going to sit there and analyze your outfit. That being said, they will notice what you wear. Wear stuff that makes you look amazing, and they'll know you look hot--they might not figure out why, though. Wear stuff that fits your personal style and makes you feel confident, and you'll be more confident and more likely to attract guys who fit your personality.
That being said, you should look all over the internet to figure out what looks good on you and what styles you like. The guys might not notice your clothing the way a girl would, but they'll notice the effect on you.
When I was in high school, the girls that caught my eye, were those that dressed differently; most girls wore jeans and some type of shirt, t-shirt, tanktop; however, the ones that had a different outfit I found fascinating, and I went after those. That was my personal preference; matter of fact, I still like women that dress differently. If a girl just likes to wear t-shirt an jeans, then hmmm, not my type. :)
I would say that for the most part guys your age won't notice a whole lot about you wear. Don't wear anything slutty or revealing. Girls think that they need to dress slutty to look good and that's not true at all. You can dress nice without being revealing. As far as jewelry, I guess it depends on the guy, but I would say that most guys would like less.
I notice clothing only if I relate too it and is attracted to it. What you wear should fit with who/ what you are and not be worn just to attract but be worn because it is comfortable and fits you, otherwise you may just find the wrong guys attracted. But generally guys don't make a whole big deal of clothing, (after all it is only a covering for the body in the most basic sense, sorry for fashion freaks).