I’m new to the game. Haven’t played since Cata!
And even then not much playtime.
I’m leveling a Priest and was doing Holy but decided I don’t want to heal nor like that.
I switched to Shadow and enjoying it so far.
Only level 25 but any tips on playing and rotation outside of WoWhead and Icy Veins?
Are there any specific videos to watch like someone who is killer at the class.
Most advice people can give you isn’t really very relevant until you’re max level and doing high end content.
The one thing is just Keep Abilities on Cooldown and Always Be Casting.
Remember your ABC’s. Always Be Casting.
Right now you’re low level so there’s not much gameplay advice people can give you. The basics are basically:
I find it helps to get into a bit of a rhythm. You’ll notice Power Word: Shield is a super low cooldown. I usually time out 4 casts, on the 5th self-shield, 4 casts, 5th self-shield etc. Very rarely am I not one of the last people (if not the last person) up. The survivability is nice, because priest mobility sucks badly.
Beyond that, I prefer Mind Spike, but Mind Flay isn’t a bad choice, either. If it hasn’t changed, the difference in damage is so low that you should just use whichever feels most comfortable to you.
It has indeed changed.
If you are playing voidweaver, you kinda have to play spike.
If you’re playing archon, you have to play flay.
C’moon, don’t be so strict. 
Incidentally, I’m playing voidweaver, but man that kinda sucks you can’t just choose these days.
Honestly I’d love for Shadow as a spec to get a legitimate good redesign, like what they’d done for Ret. I kinda feel like it could very much use the ol’ developer scrub-a-dub.
I think giving both playstyles their own niches and distinct feels is the best you can realistically hope for there.
Expecting every talent to be equally viable with every other talent is just going to erode the interactions and distinctions they have that separate them in the first place. Mind spike has all the mind blast interactions, and voidweaver buffs mind blast and plays around maximising the value of it.
The two of them should do different things and feel different to use, which in turn is going to affect what they’re good and bad at / play well with. Same with Dark Ascension and Voidform.
Just a personal question for fun:
Would you prefer a complete redesign where they scrap the two co-existing faces of Shadow to make something completely new, like a Legion-size rework? Could be risky but it could also turn out to be pretty good.
Or do you prefer having both DA+Spike / Voidform parallel so that everyone can chose their preferred playstyle? Is a bit tough to balance but many people love Voidform and hate DA and vica versa.
I think we’re honestly in a pretty decent place on single target with two different playstyles that serve two different sides of the spec and play very distinctly.
AoE needs work, not necessarily a return of mind sear or AoE spender but I think that’s the main pain point.
I think Shadow has the best designed hero talents in the entire game.
Honestly, pie in the sky wishes for me would be an actual mobility choice node shared with Life Grip. Maybe just that old Venthyr ability outta Shadowlands (door of shadows?) but with a reduced cast time (0.5 sec maybe)? I could also get down with like halved recharge on Shadow Crash, 'cuz sometimes the tank just ain’t playing ball and the extra shot would help a lot. And let’s be real, firing off more Shadow Crash absolutely will not break the meters.