1) set you npc on a non-shield job
2) find the toughest mobs out there that you can solo with ease, but still at least 10 levels above your npc
3) talk to your NPC every day at the rendezvous point
someone else may need to detail the quests... they help with leveling the NPC
from NPC lvl 30-50 the exp it earns is capped on mobs 4 lvls higher than your npc. for example your npc is lvl 30. you much fight a lvl 34 mob to get max exp. Lvling it on mobs 10 lvls higher is pointless.