Set up TSM properly, learn it well and I can already see the power potential it has. Second is diversify your markets, learn other markets and the more you set up the more potential profit you have. Third is probably leveling alts so you have a wide range of professions ready to tackle any future opportunities for profit. Forth read patch notes religiously.
Hazzikostas said his top recommendation prior to the BfA prepatch would be beating the Mage Tower challenges for those special artifact appearances. Not only are those some of the most attractive weapon skins in game, but the Mage Tower challenges will be going away when the prepatch hits, so you've only got a couple of weeks left to complete them.
Changes were also made to levelling in earlier content with Legion's 7.3.5 patch. The level-scaling tech introduced in Legion not only be continued in the new continents of Kul Tiras and Zandalar, but was also be applied to content from prior expansions, allowing larger level brackets for lower level zones. Further, as previous expansions are now included in the base game, the level ranges for those expansions are now broadened, allowing players to spend more time leveling in preferred expansions and avoid others entirely. Some examples include a zone like Westfall having its level bracket (at 10–15 as of Legion) increased to 10–60, whilst continents such as Outland and Northrend sharing a 60–80 level bracket. The aim of this change is to encourage more player choice whilst levelling and to allow players to experience the full story of a particular zone without overlevelling the relevant quests.
Warlocks have received new spell effects; all the other classes received new effects in Legion. Male orcs are now able to toggle between the initial hunched posture and standing upright by using a barbershop, but the other races are not able to toggle between two postures. There are new druid forms for the allied races, i.e. a Zandalari troll forms are all dinosaur-based, while the Kul Tiran humans take forms made of wood and bone as their teachings come from the Drust people who populated the land before them rather than the Cenarion Circle.
Sky Golem factory; Use all your spare alts to craft those. Level their Pandaria engineering to 75 by farming ghost iron ore (mostly) and start doing their daily CD's. It's super easy to find informations on how to do it quickly, look it up. 4-5 alts = 4-5 golems a month = a million gold a month if golems go for 200k+ like on my server (250k on mine)
JC Panthers: Instead of breaking them all down like I did with the golem, I'll just note that currently on my server the Orb of Mystery and the Living Steel combined cost 36,000g. All of the panthers, except the Onyx, sell for 32,000g. A loss of 4,000g/unit, not including the gems. Once we factor those in, at a mean value of ~200g/unit, the loss per Panther jumps to 8,000g.
Professions are skills used to create and enhance items (gears). You will start with one skill once your character has learned a profession. When you use the profession, your skill will increase. A profession’s higher skill will allow you to create more powerful items. If you change a primary profession, you will lose any skill you have made with your original profession. So it is important to choose your primary professions wisely.
There's a few profession crafted pets in BfA on the horizon - Battle for Azeroth Tailoring is getting a Hot Air Balloon style pet, and BfA Alchemy looks to be getting a brand new Transmute Meat to Pet. There are some mount buff consumables from both BfA Leatherworking in the form of a mount barding, and Blacksmithing in Battle for Azeroth will be able to craft Stirrups and Hoofplates to increase mount speed and allow you to interact with things while mounted.