here is how I'm leveling:

I already have a level 50 mnk from 1.0. I'm not touching it at all this time around.
I would like to level Gladiator/Paladin this time. So, I'm using that job to go through main storyline quests.
However, I also want to level Marauder/Warrior. So for a while I occasionally used that job for main storyline quests.

I hate mage jobs, but at the same time, I want to have them available at least at a mid-level. So, I'm using each city's side quests to level those jobs. Thaumaturge is leveling off all side quests in Uldah, any fates I see as I'm going through quests and the hunting log. Arcanist is using Limsa, and Conjurer is using Gridania.

I'm not using all my quests for one class.

Right now, I'm at level 27 on Gladiator, and between 19 and 21 with the rest of my classes.
I don't expect to be able to easily take them all to 50 this way, but it spreads out the xp a little, allowing the leveling to feel less grindy at the low and mid levels.

Granted, I'm pretty sure this will change as I get to 40 and above. That's when I plan on taking some of these jobs into dungeons via duty finder Random. Get some xp, get some practice and add some variety to the FATE grinding.