i'm locked in on crafting. i maxed alchemist before any combat job. i'm only on level 92 dawntrail quests. you can level crafters and gatherers really fast with the following tips:
wait until you finish heavensward before you lock in
don't do any quests past unlocking the job until level 50
do all of your daily grand company deliveries. they give you a lot of xp
do custom deliveries for your lowest job whenever they become available.
level them all at once, gatherers first, then all your crafters. start with level 1-50, then in 10 level increments
use the +10% free company xp action, the survival/engineer guides, and crafter/gatherer food at all times
level fisher with ocean fishing. it'll level faster than anything else, so just hop on a boat whenever you get the chance and do the quests as they become available
start with leveling miner/botanist. the first 10 levels come quickly from filling in your gatherer log, from there you'll grind gatherers in the Diadem. Get them to 50, either before your crafters or at the same time. Do all your 1-50 quests after you hit 50.
then for each crafter, find the highest-level thing in your log that's easy to make (think basic ingots, thread, other things that only require 1-2 gatherable ingredients), get enough to make 99, then spam quick craft. repeat until level 50 and sell everything high quality on the market board.
once your crafters are at level 50, go on the wiki and look up all the quest turn-in items. Plug them into teamcraft or the Allagan Tools plugin on Dalamud (the craft list function is a lifesaver) and make all of them in advance. Use teamcraft or Craftimizer (another plugin) to generate macros for the high quality crafts. Then hand them all in, desynthesize all the underleveled gear and pick up level 50 tomestone gear for everything.
grind miner/botanist to 60 in the diadem, then do all the quests at once.
make all the turnins for lvl 50-60 crafter quests in advance, then turn them in in bulk. if you come up short on leveling, grab the highest-xp levequest from ishgard.
repeat the diadem strategy with 60-70 gatherers, doing the quests after.
do leves to get your crafters to 70. do the quests as they unlock (they don't give much xp and provide all the materials)
for each set of 10 levels after this, do the crystarium/sharlayan/tuliyollal deliveries on one job. level the rest with leves (or the diadem in the case of the last gatherer)