If you want speed, do the sidequests that unlock Aether Currents first. Push through main scenario quests too to get the Currents for the area.

Once you've unlocked flying for that sector, your flying speed will let you bust through sidequests easily. Some people don't like doing those but I find that there's a lot of rich stories packed into them.

There's dungeon grinding if you prefer that too. It's a good way to get yourself used to the shiny new spells you get.