Either start learning some magic and play a game of Quidditch (though I'd be useless on a broom) or start punching some trees and be terrified for night time.
I think the HP universe would be one of the best universes to live in. Not because of how awesome it is, but because it is, despite evil dark lords, rather safe.
1) Unless killed wizards are going to live for a long time. 150 years is common.
2)Magic makes a lot of illnesses and injuries painless (then again, we do have our own magical illnesses to deal with)
3) Living post DH, we have a more reformed, fairer ministry.
4) I don't have to learn any other language.
5) I don't have to get accustomed to a new type of world. Hey, I'm in Britian.
6) Quidditch
The only main problem would be if I arrive in a Book 7 universe, then again, won't be long until Mr Snakeman dies.
Either that or I best get use to running. Thats what happens when the Doctor's about...