Always check each of the prices of the item, and look over a spread of several days. This is not so important on small items, but anything that you are spending hundreds of gold on you need to check prices carefully. It is also a good idea to check a website such as Allakhazam, Goblin Workshop, Wowhead or WoWuction to see what an item normally sells for.
1. Signing Guild Charters-Many people will journey to Orgrimmar or Stormwind to get their new guild charters signed by alts and bank toons. This is where you can strike quick and fast without any risk of losing the investment! This is the greatest type of opportunity for any entrepreneur. I have seen anywhere from 5-20g per signature on these charters. This beats the heck out of earning that first hundred gold through mining copper or an alternative profession method. If you are on late at night, that is often times when the most people are looking to get this service done. Supply them with your signature!
This is an infinte farming spot that takes place just east of maraudon.   It requires you to stand in a specific spot which will allow you to kill all the slitherblade naga that surround the river.  This spot is generally a GREAT spot since the mobs respawn instantly after death.  You will get an obscene amount of silk, wool, greens, and low level patterns.  It's one of the only remaining infinite respawn farms left in the game.

Buffs. Food/Flasks/Scrolls/Potions/Elixirs are a small, but noticeable, buff to your killing speed and survivability. If you have a max level character that can already supply you with cooking or alchemy, you'll be very well off, because the AH is a cesspool for this. I can't really give you specific foods or potions to look for, since each AH is going to have different supplies. Generally speaking, lower level foods are going to only last 15-20 minutes until you can buy the more powerful versions at 60+. Look for anything that adds versatility or your primary stat, and buy stacks for each level range(1-60/70/80/90/100).
Blacksmithing is a crafting profession that uses bars obtained from melting ore to craft plate armor and weapons, as well as some assorted cosmetic items. In Legion you craft ilvl 850 gear (demonsteel), a mount and a legendary. These are the main gold making opportunities with blacksmithing. Blacksmithing can also create a lot of transmog gear from old expansion. Some rare recipes have looks that are very sought after primarily for weapons.
 Void elf - "Many have sought to harness the corruptive magic of the Void. Most who tried have fallen into madness. Determined to use this power for the good of Azeroth, Alleria Windrunner is the first mortal to succeed at defying the shadow's whispers. Coming to the aid of a group of her kin who nearly gave in to the darkness, Alleria has vowed to train these Void Elves to control the shadows within them and pledge their newfound powers to the Alliance."

Now that we have a lot to post we reached a point where we have to plan what items we post on an 12-24-48 hour cycle. The auction house fees for Warlords of Draenor items are extremely high. And the values of the items are really screwed up. A lot of the weapons or armor has an item value of 5-10.000 Gold. But they look plain bad and the chances of selling them is pretty low.