To me, the most important thing about learning vim is its grammar (verbs and objects). Check out "Your problem with Vim is that you don't grok vi." [0] (one of stackoverflow's best all time answers).
I have built my own cheat sheet over the months I have been using Vim. I highly recommend doing that after you are familar with the basics. My next step is to work on putting it in Vim itself via a documentation plugin. I got the idea from this [1] blog post.
The way I learnt vim keys was through: vim-adventures.com
This isn't a paid advertisement. I had to jump through multiple hoops to get a paid account since my country doesn't have PayPal and they wouldn't accept Bitcoin. I loved this site.
At uni, one of my physics profs allowed us to bring our own cheat sheet into exams. The point wasn't to cram it full of everything in super tiny writing, but to think about what should go on it and how to organize it. The thought process makes a bigger difference than having the cheat sheet.
[0] https://stackoverflow.com/a/1220118/2131903