Since there seems to be some confusion as to what one person can do in order to level up, I'll scrawl a few down. Please feel free to give more ideas.
*** SPECIAL NOTE 1-5 can be done prior to dungeon queues, ALSO a new class/job even for an already completed Guildhest will provide Bonus EXP ***
1. Side quests.
2. Leve quests/Grand Company quests(For enjoyment read the Quest mini-story).
3. Hunting Logs.
4. F.A.T.E.S.
5. Guildhest.
6. @15 and beyond Steps 1-5 and Dungeon's
7. Challenge Logs
I really do hope this provided some idea's for leveling, and doing other Nations GC leve Quests provides some relief of doing the same ones over and over.
-Tari