You regenerate 6 leve allowances a day. If you arent already using them to level something else, toss those into your DoL(no point being capped and not getting them). If i remember right, the appraisal leve is the best one to do. Put the difficulty level as high as you can tolerate, use your GP and drink cordials as needed. Do your class quests. Every 10 or so levels it wouldnt hurt to check if your gear is helping or hurting your progress. And if you also want to make a bit of profit while leveling, spend some extra time studying the market board for your server. There are probly a few things you can gather that sell frequently enough and for a relatively decent price. Once you find them, gather a stack or two and have your retainers list them. If you have any cheap materia put it on your gear as you level(the stat boost probly wont matter, but spiritbonding your gear faster is still a benefit), just remember to retrieve it when you upgrade said gear(converting the gear to a new materia ideally).

Oh, and it doesnt hurt to take a break from time to time. Grinding out the lower levels can be a chore.