Yeah, you basically watch them play but examine what they’re doing, even small things that you wouldn’t normally notice when watching for entertainment, like what buttons they’re pressing.
Let me give you some examples of what I have personally done. For reference, this is my first season healing as a MW and I also played some prevoker. I haven’t healed PVP since WOD.
I started by looking up rank one mistweavers, which have Mysticall and Meepmonk as the top content creators (that I know of). I largely just checked the r1 ladder and saw which ones had a Twitch I could find via Google or through the website. I used drustvar dot com
Mysticall posts on YouTube and they even have match reviews, along with actual gameplay of blitz and 3s/shuffles:
https://www.youtube.com/@MysticallTheMonk/videos
Meepmonk has plenty of streams and some youtube videos. I mainly checked his Twitch at
https://www.twitch.tv/meepmonkmw/videos
Cdew is a known healer god and they were playing prevoker, so I naturally checked them out too when I was starting up my prevoker:
https://www.twitch.tv/videos/2278094185
I learned a bit how to keep up with healing by watching how they were healing and also checking how much % of the healing each of his spells were doing whenever he hovered over the details counter. This helped me realize what order I’m supposed to rotate through cooldowns to keep people up as a prevoker. Like, echo + spiritbloom is pretty good. Echo is always the first thing he uses too no matter how low the target is because it’s simply not worth it to heal without echo. They had a constant 200k-300k DPS almost every round too because Cdew was using Fire Breath on CD.
Checking their damage count/healing count to see what % of the damage/healing is coming from which spells is also pretty good to take note of, by the way. Do this against enemy players too that you see are playing your spec well.
As an affliction warlock, you probably want to look up someone like Chanimal. There are plenty of affliction warlock streamers, I think. I personally know an affliction warlock I play with regularly and they improved a lot by watching them play. Like, from doing 200k DPS when being trained to now doing around 500k. Chanimal pulls upwards of 600k from what I’ve seen clipped