Use your main job to run through MSQ. There should be an EXP bonus on MSQ that would be enough to level you up alone. You'll be like 52-54 before you enter Ishgard for example. If you find yourself too low a level to accept the next MSQ, do daily roulettes to get that little oomph you need to level up. Try to save side quests for leveling your secondary job. Especially if your secondary job is a DPS. Queue times are murder for them. If you queue up as a DPS, you can do some side quests at the same time.