I think if you are at a level where you can comfortably use vim, the best way to learn is to just keep using vim. Whenever something feels slow, or repetitive, look online for a solution or suggestion. Then you just use it until it's learned. I don't think any advanced tutorial would be useful, since it will be a collection of very specific things done by the author of the tutorial. I wouldn't be able to remember things like that if I'm not actively using them and finding them useful for me.