I found it useful to revisit this article about what movements to expect to ride for each dressage level, and also to help assess horses to their ability and level of schooling.
Diagrams showing how dressage movements, paces & transitions are introduced as per scales of training in prelim to medium dressage tests by British Dressage
via Dressage Test Movements Prelim to Medium Level.
This is really useful for illustrating the progression of training of movements through dressage. I’m using it to get my elementary brain switched on when I’m schooling!
The Rubber Curry Comb 