Crafting is easy, it's just incredibly time consuming.
In fact, I've been spending the past few months doing nothing but crafting in the game, just because I want to max out everything. (I was tired of buying everything and losing money, plus I want to be maxed out for the company and start building a cash wad for us.)
What I've learned, no matter which one you want to start with:
-Do the main missions for your craft first. You'll eventually hit a mission lock that forces you to grind on your own until you reach the next required level (usually lvl 5, 10, 15, etc.). Also, unless the quest requires a High Quality item, don't waste your time. Just craft it and send it in.
-Then it's time to hit the fieldcraft levequests. As skill allows, this is where you want to strive making HQ items, because they double your EXP per finished quest. This jumps your levels considerably.
Usually in the 15-25 fieldcraft quests you can grind really easy, because they'll ask for 3 of something to deliver, and will continue to ask for more if you have some. This usually continues about 4 times in total, so you can just keeping crafting the same thing without having to run back to the levequest booth over and over to accept missions.
-Also note: If you have a few trades already leveled (particularly weaver, leatherworker, and goldsmith) you can probably make your own clothes. You definitely want to make HQ ones, and materia meld them when you can for more stats. This way, you really don't need to accept clothes as your optional reward at the end of main quests and can just accept the money reward (unless you want something untradeable, but that rarely comes up in crafting missions).
EDIT:
-Forgot to mention, make sure your Disciples of the Land jobs are leveled enough first (miner, botanist, fisher), usually between 15-30. Otherwise it forces you to buy material from the shops and burns money really quickly. It also gives you a chance to start digging for HQ material to work with.
They can be leveled in the same way by using main quests and fieldquests, but after working in the land classes over time, they end up grinding themselves.
EDIT:
-I would level up the leatherworker job first. It has the "Waste Not Want Not" ability, which can transfer to your other crafting jobs. It subdivides 2 of your durability turns into 4, but actually ends up giving you an extra 5 turns in total if you time it right. It's the best ability in crafting IMO.
-When making HQ items, always watch the "Normal/good/poor/excellent" status in the bottom left corner of the crafting menu. It's the roulette wheel of crafting, and lets you determine when to use a touch action to boost quality percentage (HQ.) Sometimes you're forced to give up a chance, but if you ever hit Good or Excellent and you can use a touch action, do it. The percentage will climb (tremendously with Excellent.)