Besides the missions, progression quests in the level increase xpacs, and/or fellowship...??? Grinding it out is going to be a chore no matter which way you slice it. I tend to pick up all the merc tasks in a zone, then work on hunters in that zone while grinding. So instead of just killing mobs in the same location for hours, I pick up merc tasks which are typically kill quests anyways, then pick a named camp and go start grinding there until I get the named kill. Then just keep moving around camp to camp until the hunter is done for that zone. Then I move on to the next zone and repeat. Usually, by the time I finish hunter, the merc tasks are done as well and I've gotten a solid chunk of xp.
TLDR - If I know I'm gonna grind I try to grind with a purpose beyond just killing, whole 2 birds 1 stone sort of thing.