Where is the First Aid Trainer, and how do I advance?

From wow.incgamers.com

First Aid trainers are found in or near most staring areas, and you can always ask in cities for directions to the trainers there. See our First Aid Page for a full list of all the trainers.

Once you get into the expansions though, they can be harder to find!

Outland

The First Aid trainer in Outland is in the Temple Of Telhamat (Alliance) or Falcon Watch (Horde), both in Hellfire Peninsula. You have to purchase the book [Master First Aid - Doctor in the House], allowing you gain Master skill (300-375). While you are there, you may as well buy [Manual: Netherweave Bandage] (First Aid skill 330) and [Manual: Heavy Netherweave Bandage] (First Aid skill 360, because you will level the skill quickly in Outland with the high amount of [Netherweave Cloth] that drops.

You will need plenty of [Runecloth] to advance from 300 to 330, but Runecloth drops from a lot of mobs in Hellfire Peninsula, along with Netherweave, for your next lot of bandages.

Also you can level on [Powerful Anti-Venom] which will be yellow even after [Heavy Runecloth Bandage] is green - the ingredient is [Huge Venom Sac].

Northrend

Details to come.