Blacksmiths: Farm Pandaria mobs until you get the Balanced Trillium Ingot plans - craft one!
Engineers: Farm Pandaria mobs until you get Chief Engineer Jard's Journal and learn the recipes from it. Pop your Blingtron daily for a chance at the new Lil Bling pet!
Scribes: Farm Pandaria mobs to collect new Glyph recipes as well as the Crafted Medallion of Tenacity.
Leatherworkers: Farm Pandaria mobs for the Hardened Magnificent Hide recipe as well as the Drums of Rage recipe.
Tailors: Farm Pandaria mobs for the the Celestial Cloth recipe and craft one to learn a random Crafted Malevolent recipe.
Cooks: Visit the Timeless Isle to start the quest chain for Noodle Carts! I'm sad to say that I was not able to put this post together in time for the patch. I got stuck on the stupid Jade Temple boss and could not kill him. Unfortunately on the PTR player gear was scaled down to 463 inside the 85 dungeons. I have no idea if this will be the case when 5.4 goes live.
For now, you can review my notes on the quest chain leading up to this fight:
To unlock the starter quest, you'll need to head for the Timeless Isle. In the center of the island is Moss Green Lake. If you head east from the north side of the lake, you'll see a broken bridge in between two rock formations. This spot is called "Red Stone Run" on your mini map.
You want to head east from the lake to the top end of the bridge on the map. In reality you'll be under the bridge at ground level, not on the bridge itself. Right at the broken bridge is a quest object called an "old sign fragment". Just pick it up to start the quest.
Next you'll head southwest to the small village called Old Pi'jiu. This is the same village you probably rode past when you flew to the Isle (if you are Alliance). It's infested with spectral pandaren, so be prepared to fight your way in. I was able to use stealth to reach the NPC and turn in the quest. She will give you a new quest, this one requires you to kill the Sha of Doubt at the Jade Temple.
I'm not sure I'm thrilled with this idea of being required to kill dungeon bosses for recipes, but I'm reserving judgement until the end of the chain. I tried stealthing through the Jade Temple but apparently you can't get beyond the second boss without completing that fight.
Kill the Sha of Doubt, then turn in the quest on the patio behind (Lin Family Scroll). Don't leave the Jade Temple because you also need to kill a ghost panda named Lin Da-Gu. He's a level 90 elite with 7878k health. I don't know if this fight will be possible to solo. When I tried it on the PTR my gear was scaled down to 463.
UPDATE: Reports are coming in that the new crafted epics were changed to BOE. Don't forget to use your cooldowns and learn those recipes!!
Feel free to leave additional hints and tips in the Comments for others!