Others will touch on talents, traits, essences, gear etc.
My advice is get your rotation right. #1 priority on every new character I make. You want to make sure you know HOW to maximize your damage, and executing your rotation properly is how you’ll do this. Otherwise all the gear in the world won’t matter and you risk being one of the many 475 ilvl players who can only put out like 40k instead of double that.
Go to raidbots website (google it) - click “Stat Weights”. Look up your character. Once selected, under the options expander (down the page) select Patchwork, 1 boss, 3 minutes.
Make SURE you select “no buffs” as the point of this exercise is to get your rotation right, and you can then do this by practicing on target dummies without having to buff, flask, heroism every try.
Find the 120 boss target dummy in your BFA city (google it if don’t know).
When it spits out your estimated dps, what I do is not leave the target dummy until I can get within 1-2k of this over the 3min fight. Then I know that i’m doing the rotation mostly correctly.
In your sim, once it’s generated, you can click down the bottom right of the page the “Full HTML report”. This will tell you things such as what % of your damage comes from what abilities. You can then check your damage meter logs on the boss dummy to highlight any basic mistakes to you. If the sim says a certain ability should be 10% of your damage but it’s only 5%, you now know you’re making some mistakes to do with that ability.
There’s also “sample sequence tables” in the repprt, which can help show you maximum dps openers and ability orders (in conjunction with your spec guide).
All of the above should be used after reading, and referring back to, your spec rotation guide on Icy Veins or Wowhead. Most people just read the guides, and then think they know the rotation, and proceed to be terrible. Don’t be them.
Almost nobody puts in the minimal amount of time and brain power to get their rotation correct like this. If you do, you will out dps the vast majority of people at the same ilvl, all for about 1hrs time investment.