One thing to note, you can get one job to max level with a combination of quests, Hunting Logs, and FATEs but levelling subsequent jobs is a real pain in the ***** Depending on your job choice you could spend over an hour to queue for an instance that will yield you around a third of a level and chasing FATEs around zones and spamming abilities on mobs that often don't even appear on your screen gets old very fast.
^ This one is doing it wrong. Let these ones explain.
The key component in getting through leveling secondary classes is having people with you. Queues are instant if you have a healer, or bring a healer with you, and dungeons can give you a whole levels worth with rested XP, Chains, and the 50% XP Bonus you get for leveling classes that are lower in level than your highest.
FATES are hands down the fastest XP in a party, FATES that involve killing lots of enemies tend to yeild great XP when you're netting XP from claims everyone in your party manages to tag - letting you net 2 levels in as many hours if you are lucky. There are frequent 'hubs' in which people gather together to do FATEs together in parties with, you need only shout for an invite.
Some of the camps I remember off hand, and this is not a complete list.
Costa De Sol
Cerelium Processing Plant
The point is not to get burnt out. There are seasonal events, crafting, and just chilling out to do. Right now endgame is pretty sparse due to it being before any content updates. Play casual, don't forget your favorite TV shows, play some other games once in a while and don't sweat falling behind, as the entire system in endgame is sort of a treadmill anyways.