Most Helpful Girl
First thing first, get a nice hair cut, that's the fastest way to change your style. If you wear glasses (all the time), try contact lens if you haven't already. I suggest go to store and look at how people mix and match outfits for mannequins and decide what kind of style that suits you most. Sorry to ask this, how much do you weigh currently? The best thing is to get the right size of clothes, if you don't like outfit that expose too much, try longer ones and add a belt, you'll look good.
Just don't be afraid to try on different styles, you'll figure out more what style suit you best eventually. Good luck :)