Hillsbrad Foothills is just simply the best place to farm Tin. If you are an alliance player you should still go there, but Northern Stranglethorn is a great alternative. You will see a red zone on the map, that zone is filled with Tin, it's everywhere. When you mined all of it, just go outside of the zone where you can see the little yellowish arrows, mine a few Tin and head back to the red zone because it's most likely that the Tin Veins there are already respawned.
The world quests aren’t necessarily bad, but they aren’t good either. I wouldn’t mind killing five of a type of monster or fighting one particular boss a few times, but after seven or eight, it starts to wear pretty thin. But going from levels in the mid-20s can take nearly 30,000 AP, so you’ll need more than world quests if you want to get your heart up in a reasonable time.