The best way to collect AP is through world quests, a system that allows players to complete menial tasks to earn moderate rewards. A finite amount of AP spawns on the map through these quests — generally at least 2,000 a day. I’ve likely done most of these quests close to 20 times in the course of preparing my various characters in the 45 days since the expansion launched. In some cases, I’ve replayed them as many as 50 times.
Now, on the other part of the equation, the items that return materials on mission finished are overlooked. Looking at this Wowhead comment https://www.wowhead.com/item=162114/crimson-ink-well#comments:id=2607578 the most lucrative ones are the disenchanting rod (returns enchanting mats, best case scenario, 10x veiled crystals) and the magnetic mining pick (returns ores, up to 40x Stormsilver). This is totally server dependant, but you will need to check which ones are worth where you play.
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Herbalism is also a good source of money. Herbs are required by alchemists and scribes. Unlike ore which is found only in rocky areas, herbs can be found in many places. Be sure to check on the auction house for what herbs are in demand for a high value; often a lower level one is very valuable, so you can farm an area you already know for quick money.
To give you some perspective I leveled both a LF Ret Paladin and BE Rogue (so one started from level 20 and the other from level 1). I focused on getting the achievements I was missing for the Loremaster, so not the most efficient route by any means. I was using full enchanted heirlooms (minus the ring) and the WoW-Pro addon though, as well as having War Mode turned on all the way.
At Level 18, you unlock Freezing Trap which is a long-term crowd control for all Hunter specs. It places a trap on the ground that encases the first enemy (not bosses or most big encounter adds) to touch it in ice for 1 minute. The effect breaks on damage. The trap has a 30-second cooldown, and the trap will exist for 1 minute after placing it. This is useful when you are feeling overwhelmed by too many mobs, for temporarily taking out a powerful mob from the fight.
Jewelcrafting is a crafting profession that revolves around gems. You prospect various ores turning them into gems and cut the gems. The cut gems can be added to socketed items. In addition you can craft rings that can either be disenchanted or sold as gearr. The Legion epic and rare gems and rings all sell very well. The jewelcrafting panther mounts are the best old world recipes.
Get exalted reputation with every faction you can. This relates to the previous two pretty directly. Gaining reputation with most of the factions of Kul Tiras and Zandalar will allow them to sell you high-level gear, while gaining reputation with the Champions of Azeroth faction will grant you levels for your Heart of Azeroth, the neck piece where all of your AP is stored.
EXCEPTION: If you are leveling trade skills while advancing, review the materials requirements of every recipe, pattern, plan, or formula that are planning on purchasing from a trainer. For example, some of the shirt patterns for tailors use very few materials and thus yield a more efficient manner of leveling the trade skill. Check profession leveling guides here on the wiki, ask a guild-mate or friend, or check out information on other web sites to help in this area. A little pre-planning and fore-thought can save you huge investment costs in the long run.
Improper leveling of your production profession skills can cost a small fortune. Heck, even proper leveling of some production skills can cost a small fortune. And keep in mind that equipment you produce using your profession will typically be slightly worse than equipment otherwise obtainable at your level via the Auction House and/or instances. It is therefore strongly recommended not to take on a production trade skill until you hit at least level 30, or better yet, level 70+. However, if you are determined to take on such a profession (particularly under level 30), read a suitable leveling guide in order to gain whatever skill level you desire for the least amount of money.
If there would be a transmog server #1, all transmog vendors would transfer there and the market would get destroyed fairly quick. In general, Roleplay-Servers like Argent Dawn or The Aldor are better server for selling transmog. On high pop servers you have a lot of other players selling stuff and as a result, low prices. On low pop servers prices are acceptable, but you have no buyers. So there is not recommendation for a server really. Its up to you.