The stranglethorn quests are nice to gain a lvl or two. Be certain you've cleaned up all the Darkshire quests as some will still net decent exp for very little trouble - I might say the same to a lesser extent about wetlands (way green and lots of running, but it works). Be sure to complete the missing diplomat quest line . . . it's a lot of running, but it's pretty nice exp toward the end of the line and it will get you to dustwallow. Dustwallow is quest rich, southshore is quest rich, badlands only has a couple quests but would provide a grind spot if that's what you enjoy (with a nice little trinket: Nifty stopwatch obtainable @ about 38 - the cash isn't bad either). Also, quest out SM as best as you can. It's close to southshore which is convenient.
I think the best way is to have a plan, grab the nearest person and go have fun. When you have two people, a TON more is possible, hillarious, and sometimes more challenging than solo, and the exp ticks by super quick.