77 Mage here.
Not sure if anyone posted this earlier.
But being a newb to this game, I'd share something:
You can accumulate more than one task. How? (and it's not a glitch) You just take the recommended task that of each zone for your level, and DO NOT complete them. If you do complete one, you're locked out from taking more tasks.
However, once you've gotten all the tasks you want to bank. Then start doing them all. You will net a huge amount of exp in a short bit of time.
Being a 77 Mage, I simply did the level 70 and 75 task to see how much I got, turns out I got 20% exp towards level 78! All that from killing 10 things...
So in case you didn't realize it or it wasn't mentioned above. You can accumulate multiple tasks.
I will try for all the 50 to 75 tasks for more exp tomorrow...
Have fun!