Check the Auction House prices using the search facility in game

Keep notes of how much a stack of resources (light leather from skinning, copper ore from mining, silver-leaf and peace-blossom from herbalism) sell Last Chaos Gold to an NPC vendor but don’t sell to the vendor.

Check the Auction House prices using the search facility and take note of the starting and buyout prices for the stacks of resources you are selling. Many items have a buy-out price up to 10-20 times the price an NPC vendor will buy from you.

I personally set my prices as follows starting price 2x the NPC vendor buy value (around 1.5-2.5s per stack) and a buyout price 5-6 times the NPC buy value unless all the competitor sellers buyout prices are way above or below that, then I set my buyouts at just below theirs.

A couple of hours work at toon level 6-8 will give you 3-4 stacks of light leather, 2-3 stacks of herbs, 1-2 stacks or metals bars (yep, smelt them for mining experience before selling them ... if you are "grey" on smelting copper (ie no mining XP form it), sell the stacks of raw ore) and if you are working in an area of humanoids 1-2 stacks of linen cloth.

Don’t waste your linen on bandages (First Aid) at least not yet, players are able to be a merchant who can sell products and gain WoW gold.