What levels do you have to be for which quests?
A guide or something might be helpful.

clobber

The NPC's will assign you a task when you are ready for it.  Just keep going back and checking

There are also several Player guides that you can find links to in the Documentation section, these may have some information that you can use.

Other than that, pay attention to what the NPC's say, talk to them every few levels, watch the message box for a message that says something along the lines of " You just got *suchnsuch* quest item."  OR when examining an item it tells you its a one drop item, thats a sure sign its a quest item, though you will have to run the whole list of NPC's when you are the right level to see which item goes to which NPC.