Sell your gathered items as soon as you can.
Your biggest earning day for the entire MoP expansion will be day 1 of MoP.
Your 2nd biggest day for the entire MoP expansion will be day 2.
Your next biggest day will be day 3.
It will continue like this for the first couple of weeks; where finally you will start seeing gathering days followed by consumption days.
What does this mean to you? Day 1: Miners and Herbalists : level only by gathering. Traditionally, 1 node is worth 4 mobs of XP in the same area. Skinners; skin everything. Picked up meat, cloth? Then sell that too.
Have a banking alt sitting next to a mail box and auction house. Every opportunity mail your loot back to your bank alt, and post it on the auction house. At least daily if not more often.
Ask a lot. At first, the demand will outstrip supply. Secretly - what would you rather be doing? Gathering or exploring new quests. So will the other gatherers. There will be rich buyers out there with nothing to buy.
Some guildies will ask you to donate to the guild bank; so next month they can start leveling their tradeskills. SELL YOUR STUFF NOW AND DONATE LATER.
Sell everything as soon as you get it. If you feel generous, buy it back again in a month's time when prices have dropped. If you feel inclined; you will be able to donate more than you had gathered, with a nice weight of gold sitting in your pockets.
Gatherers; the start of an expansion is your time to earn. The gathering bots have not yet been written.
Go make hay while the sun shines.
Don't bother farming WOD raids/dungeons for gold! - Public service announcement for anyone who does not yet know! Don't bother entering Warlods of Draenor dungeons with farming gold or transmogs in mind. The...
7 hours ago