Up to 50: Ixali dailies, levequests, grand company turn-ins, grinding.
50 – 70: Custom deliveries, Moogle(50-60) and namazu (60-70) dailies, levequests, collectables, grinding, grand company turn-ins
70+: Crystarium deliveries, custom deliveries, levequests, collectables, grinding, grand company turn-ins
This is what I did, in order of preference. I only did the grand company turn-ins and levequests/ collectables when I didn’t need to spend half the day gathering mats for them. Collectables with easily obtainable mats are especially good for grinding as they don’t have a limit and they provide yellow scrips to get the manuals.
Always do class quests. I usually spent the first part of every expansion making HQ versions of the starter gear to take me through the xpac.