1st, do 1-15 on your own, all the matts for the early levels are cheap & sold by npc vendors. The 1st class quests give you a massive shard influx. Do armorer last.

Next, level GSM to 50. Flawless Synthesis is helpful at early levels.

Unlock your challenge log, Limsa (Drowning Wench Quest.)

Do your GC provision quests everyday, and buy xp boost manuals with seals.

Do your ixali dailies. (Fallgourd Float)

Grinding: items you've never done before = xp bonus. Sell HQ leve quest turn in items.

The above = best bang per gil.

Then, Fuel your leveling with money. Find a crafter and see if they will mass produce HQ leve quest items. I normally do 1/2 board price. Shout for help & likely find people to do it cheaper/free.

If you have 99 leves to burn, as well as 400-1million gil. Take the crafter-in-a-box option that Mariene Vintrielle developed. It's well worth it. As a fresh 50 you'll make it back in a week or less.