It's been a while: Quests and multiple jobs?

[Squintina]

Hmm well there's:

All levels: Check out the challenge log. Check out your class's hunt log. Every 5 levels do your class/job quests, they give out a bit of exp and sometimes useful skills.

For 1-10 I'd use hunts and whatever levequests you pass by while doing those hunts (If you left the game for a while you probably have a ton of allowances)
10-15 Do guildhests (Duty finder) and/or Leves
15+: Dungeons, Daily roulettes if not done already. Tank/heal classes will get fast queues, DPS won't. FATEs while waiting. Leves if you want to as well.
30+: same as 15+ but fates become decently viable because lots of people fate farm in Coerthas, so the fates spawn faster, end faster. If you know what you're doing, you can get a lot of gold ratings (max fate exp) when there are other players doing fates with you. If you're in a party, you also get exp for the mobs they kill if it's a fate that has mob waves. Check out the party finder if you're trying to find fate parties or create your own.

^ For the hunts, leves, and fates I would also have the chocobo companion out so it can work toward the challenge log. If it's a leve that requires /soothe, put it on follow. Chocobo might kill your targets even though they're supposed to be left alive.

And since you already have a high level class/job, you get an exp bonus!
Other tips: use food for 3% exp. See if your FC can put on exp buff. Log out in sanctuaries for rested exp when you come back.

Other people might disagree regarding whether to use leves at all and just focus on fates. Up to you what you like best. I like the low level leves because they're nearby (no waiting to spawn) and once I do them all, I use the return to do it all over again. I use whatever is recommended +1 so that it gives more exp without being too challenging but you can go for more if you want. Kill wanted monsters if they show up during the leve.