Get everything to level 15, then focus Culinarian up to level 37 for the cross class ability Steady Hand II. Your primary instruments of low level leveling are Tricks of the Trade (Alchemist 15), Hasty Touch (Culinarian 15), Steady Hand II (Culinarian 37). As you level every 5 levels, you gain an additional cross class ability slot so you can add more as you go along.
Some people max Carpenter first to gain the CRP 50 ability, but it's possible to level across the board (I did) in increments of 5. Vertical leveling will get you to 50 probably faster, but horizontal leveling saves some money since you can make the materials you need across classes. The smartest (and laziest) method of leveling crafting is to hog a crafter at 50 of the class you want to level, and force them to make all of your HQ leve items, so you can dance around at your leisure instead.
I think of crafting as a turn based game, where you have a limited number of turns (Durability) to make as much Quality as you can and still have room left over to complete Progress. The cross class skills do various things to help in this process, like recovering CP, increasing success rate, recovering Durability (so you have more 'turns').
If you want to max out crafts, you have to burn leves.
This is a good place to look up what leves are available, complete with information on the exp granted by each leve and the locations. If you produce an HQ item to hand in, the exp granted is doubled.