Keep doing story quests, they give lots of EXP.
Run your daily leveling roulette, once/day will give the bonus and it's a HUGE bonus so...make sure to do it.
If you get to the dead-level area with not many story quests, run dungeons (the highest level you have unlocked, so try and go unlock Dzemael Darkhold or Aurum Vale which give good EXP).
Do your hunting log, too, if you haven't been.

If you have some downtime between dungeons, which as a WHM you shouldn't have much of, do FATEs or sidequests, whichever you think is more fun.

Have fun