Generally I just spec tank/healer and sit in a main city queueing for randoms to level my alts. My Brewmaster Monk is 71 now just chaining instances since 15, it's been like a week with like 15 hours played or something. If I get a long instance I've already done I just leave and log out for 30 minutes to wait out my debuff.
Questing is absurdly boring and tedious, doing instances isn't too bad. And if you're a tank you can basically solo everything (at least I can on my Monk) so it doesn't matter much what your group is doing, and if you're a healer you can help do DPS since most DPS are terribad leveling up. If you happen to be playing a pure DPS class then find a friend to queue as a tank/healer haha.