While yes, this might be pretty much common sense or this method was already posted (not in the past weeks from what I've searched tho), I actually wanted to share this with you guys as nowadays prices of enchanting mats are insanely cheap, giving the opportunity for some pretty nice profits.
Basically, you guys should focus on the most expensive enchants currently in your server's AH, but also, focus on those that you're assuming are most likely to sell (such as enchants that are used on twinks / mop leveling, etc). For instance, a lot of people that used +crit on bracers in high-end Cata raiding are most likely to use +haste now for quick leveling, same with expertise for tanks, etc.
I'm going to share some screenshots from my realm's AH, the prices were actually way lower but I've bought the ones and just thought of taking a screenshot now.
https://i.imgur.com/BQK6o.png
https://i.imgur.com/CZB02.png
https://i.imgur.com/4B7ba.png
https://i.imgur.com/FVDap.png
https://i.imgur.com/u8tjI.png
https://i.imgur.com/lN0CY.png
Good luck!