Chronologically?
It’s a bit “broken” as of today, as you won’t move in a straight line in the timeline while questing…
I’ll explain.
You start your adventures shortly after the Cataclysm, the even where Deathwing arose again and started his quest to destroy the world.
Which is why you’ll see many references to the Cataclysm and Deathwing while you are questing up to level 60.
When you reach level 60 you’ll choose between going to Outland or Northrend.
Outland is the Burning Crusade expansion which is the first expansion.
Northrend is the Wrath of the Lich King which is the second expansion.
Both of these take place before the Cataclysm, which is technically the third expansion.
Once you’ve reached level 80 you’ll choose between the Cataclysm and Pandaria.
Cataclysm returns you to the Cataclysm, which is the third expansion.
Pandaria is Mists of Pandaria which is the fourth expansion.
Once you reach level 90 you’ll go to Draenor.
Warlords of Draenor is the fifth expansion.
Then when you reach level 100 you’ll go to the Broken Isles.
Legion is the sixth expansion.
Then upon reaching level 110 you’ll go to Kul Tiras/Zandalar
Battle for Azeroth being the seventh and newest expansion.
So as you see, you won’t be able to chronologically go through each expansion. As the original quests were removed and replaced with a “Cataclysm” world.
So you’ll go “back in time” for The Burning Crusade or Wrath of the Lich King, then “forwards in time” again for the Cataclysm or Mists of Pandaria.
When Shadowlands is released they’ll revamp the leveling system, so that you’ll choose which expansion you want to level up in. Then move on to Shadowlands after that.
While new players will be forced to level in Battle for Azeroth since it is the closest in the story to Shadowlands.
Any character they make after they’ve reached max level on one will be able to choose where to level up.
The idea is to pick an expansion and see the entire story, instead of going to one then outleveling it and moving on to the next before you’re halfway through.
So don’t worry about doing things chronologically for now, just go where you want to, and pick what looks most interesting. The 100% XP boost will make you outlevel any expansion before you get to see it to completion anyway.
Good luck and have fun 