Hi Paishiya,
First off, welcome back! You came back at a wonderful time with 8.3 having been released this week! With 8.3, comes plenty of new activities as well as older ones!
The first thing I would suggest is continuing to work on your Mechagon and Najzatar zones. You already have benthic gear and upgrades from elsewhere, so you don’t need to do it gear wise, but the essences (8.3 has updated ones for corruption purposes), rep and fun items like mounts and pets can be worth it.
Island Expeditions reward a significant amount of azerite power each week you complete the quest, and with the catch up mechanics currently in place, it can help with your neck level. There’s also chances for pets, mounts and other items on the islands themselves or through the dubloon trader. See if you can get into a Mythic group, so you’ll only need to do 3 a week to complete the quest.
The warfronts, especially in heroic mode, can land you some nifty gear. They take a while, unless you have a group that can coordinate. They’re fun too!
Make sure to start your quest line for your legendary cloak. The assaults as you go through it will give you some decent catch up gear, you’ll learn about all the corruption and you’ll begin your visions grind. The horrific visions, once you get to that point, will allow you to upgrade your cloak as you go, which is what you need to do, grinding wise.
The new raid, if you’re interested in that, will open on Tuesday.
Otherwise, you have your other older content which people still do, such as Mythic Keys (season 4 starts Tuesday).
Hopefully that helps you out a bit!