Basic Expression Workshop: https://youtu.be/aZ5F1eCm428
the best way to learn expressions is to use them consistently with your projects. I hope you like math hahaha; it helps. Personally, I think that coding has an affinity with people who like math and organization
Here is my recommended learning path: watch the Expression workshop video for a quick overview and then watch Animoplex tutorials
Not necessarily, while a foundation in JSX helps, you can easily learn that as you are learning expressions. I often refer to w3schools to look the the functions documentation. There are a lot of them but you only need a handful eg. variables, arrays, string, operators, loops, conditional, function, math, or random. If you can understand these concepts, expression can be a breeze.
Absolutely NO. You do not have to be good, you just need to know the important ones (eg. Not Inherit Scale from Parent). Most of the master-studies tutorials (with the exception of Ordinary Folk's ones) uses basic expression to do make things look "complex". Here is an example
Flatwhite Motion wOo video: uses one of line expression of valueAtTime
Flatwhite Motion Aicy Flying Orb: uses a detailed wiggle function
Creativity by Jose Pena 32-36s: uses "Not inherit scale from parent"
Not really, I would say there is the School of Motion's Expression course but I never taken it before. I actually got better at expressions when I was learning scripting instead. Maybe you can give that a try.
Play: Personally, I really enjoyed Mathematics, it was my strongest and favorite subject in school. I love solving riddle and discovering patterns and that is how I see expressions: They are just are fun riddles. Usually I would get an idea about an expression to animate or design something, and I would spend lots of time and effort figuring it out even if I was not going to use for any current projects. Hence, fun is an element when it comes to learning!
Make your library. There are just way too many expressions to write or remember, that is why I have this wiki site to house everything. I recommend anyone who want to get good at expression to start their own wiki page and curate your own code snippets you found or wrote yourself. You can use Gitbook like me or Google Sheets like JR Canesto.
Just do it. When I first started, I would type out expressions from tutorial and avoid copying and pasting. Even if I do not understand what I am typing, I am building the coding ability into my subconscious.