Go through your crafting log and craft 1 of each item until 15. If you're leveling a job that doesn't have enough recipes to hit 15 this way, quick synth a cheap recipe afterwards until 15. After you hit 15 just do the level-appropriate courier leves all the way to 50. In general is take 8-10 courier leves per 5 levels. Double if you can't HQ the item.

http://ffxivcrafting.com/levequests