Casual or hardcore, there's little excuse for not knowing how to play your class. We all have lives outside of Azeroth and the WoW community knows it. That's why there are so many guides available to help you be the best you can be at playing your class.
There are several places to go for guidance. Icy Veins and WoWhead are classic go-to guide sites for class specialization, talents, gear and best in slot items (BiS). And my favorite place to go to for all things priest is Warcraft Priests. The website formerly known as HowToPriest is now Warcraft Priests. They've been the best place to go for guides, getting started and macros for playing all three specializations: Holy, Discipline and Shadow. Warcraft Priests' Discord is very active, friendly and helpful.
For raid and dungeon fights, go to Fatboss TV to watch and study boss fights. Don't forget to check out the commentary from some amazing WoW players via their Twitch channels as well. For example, Midnah is arguably one of the best druid healers around. She's a small time streamer but incredibly knowledgeable about Restoration Druids.
Like most WoW players eagerly anticipating Battle for Azeroth, you'll likely be sitting for hours at a time leveling. You're looking over your guides and you're ready to jump into action. You're gonna need sustenance. By sustenance, we mean food--keyboard-safe snacks like:
Nuts, if you're not allergic to them.
Fruit. Bananas, berries, already chopped melon and pineapple, sliced apples
Celery with your favorite dip.
Dry cereal. Frosted Flakes and Captain Crunch Crunch Berries or whatever you prefer.
WoW isn't one of those games you can just pause. You have to get to a safe spot before going AFK. Sometimes, that can take a while, especially if you've already been going at questing and running dungeons or raiding for hours already. Don't forget to stretch, walk around for a few minutes. Hell, if you're worried about your weight, do 10 squats every hour or 10 push-up or 10 crunches. Set an alarm or timer to remind you that you need to get up and get your blood circulating.
Share with us how you get ready for WoW expansions.