I was never able to perform at my best just trying to cold follow class/rotation guides.
When I was still playing, if a newish player to end-game of MMOs mentioned that they were ready to take their first baby steps out of super casual tier, my advice for them was to follow what I did for all the classes I cared about.
1. Get a roulette buddy to stick with you for several weeks
2. Make YoshiP cry and download ACT
3. Engage in friendly competition with your roulette buddy to try and beat each other (if both of you are DPS) or use them as an accountability partner to encourage you to keep getting better as you go
4. Mix up what you que as every once in a while to see how others perform in your role and compare your numbers to them
5. After you've got a good feeling for what works and pumps out decent numbers, THEN go get the flowchart/class guides and use them to see if there's anything you overlooked while naturally learning the class
6. Fix any mistakes you were making and practice in future roulettes
7. Get as much of your rotation as you can in muscle memory and set your UI up so you can see your cooldowns easily
8. Congratulations! You are now ready to stick your feet in savage or attempt the harder solo challenges. If you did steps 3-7 enough times you'll blow 95% of the population of the water at your gear level just from practice alone.
I've found the simple idea of having someone there to ensure you can't slack off even in casual content helps force the learning experiance along much better.
That said, this method is totally incompatible with most people who want results ASAP, but I think the results and feeling of comfort you'll have with your job will speak for themselves.