[Junebaby]

One great way to make clothes look better is to check the sleeve and hem length. If the sleeves are too long and it's a simple hem, not a cuff, you can turn it up and do a hem stitch. If you can't sew get a friend to teach you or trade a favor. If you have an old top that's frayed on the bottom or too long pants that you wore anyway, doing a hem at the correct length will improve your appearance.
If you find a quality item at a second-hand store or clearance rack, consider finding a tailor and investing in alterations.
If you're a woman and are tired of a blouse that's still nice, replace the buttons with something different. Each button could be a different color, or just upgrade from white plastic to a nice metallic.