Unless you live somewhere cold I wouldn't recommend wearing tights or anything because you'll overheat and be VERY uncomfortable.
Chances are, you notice bruises/scars more than other people will. It's not uncommon to have them from sports and the like, so I wouldn't try too hard to cover them up. If you're talking about like, a surgery scar or something, try consulting a dermatologist if you can, or tru a product like Mederma to fade them. I've heard many different stories about if it works or not, but it's not wicked expensive so you might as well try.
As a side note, if you don't obsess over them too much, no one else will either. Wear your dress with confidence, do your hair in your favorite style, & you'll look and feel great!
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