Having quit and just recently come back no one I used to play with is active, and trying to find consistant people was an issue. Honestly though you are going to have to try and play with a ton of people, find people you enjoy playing with and enjoy talking to, people with the same mindset and around same age always helps. I can't deal with some 13 year old constantly bragging about how good he is.
Eventually get in with a good pvp guild that has alot of players, play arena with some prove yourself and then everyone will start asking to play with you. Then you will be able to be more selective, my suggestion though is do not be an arean snob, be humble and play with as many people as you can. Be honest on experiance too, I had to be brutally honest with people, telling them although in WotLK I was a 2700+ player, but in mop I didn't know jack, some people will say screw it, other will work with you.