Well the benefits are pretty obvious, you have straight teeth that 'feel right' in your mouth.
You'll get told most of this when you get them but avoid hard chocolate, boiled sweets, toffee, basically anything that'll stick to your teeth or braces. At best it's uncomfortable and at worst you can rip your brace off so yeah, don't have 'em for a while.
So far as things you should know, all I can think of is to make ABSOLUTELY SURE that you brush your teeth and braces properly. Bits of food can get caught behind the wire and other bits of metal and, if not brushed away, you'll get ugly brown stains on your teeth in the shape of braces. Oh, if your dentist/orthodontist has them, get a special toothbrush for people with braces, they're a life saver. Also, no mechanical toothbrushes, learnt that the hard way.
One last thing as a heads-up, your braces can catch on your lips something mean sometimes. I don't know if everywhere does this but ask for some wax after you get them fitted if they don't give you any. Make a small ball of wax in your fingers and apply to the part of the brace grieving you (if it happens, you'll know exactly what I mean).
Other than that, braces really aren't so bad. Like before, I don't know if everywhere does this but I could have my braces a different colour every time I had them tightened or checked up so be creative and have fun with them!
EDIT: Damn, everyone else got there before me with quicker, shorter posts :/