Development environment
Clone, build the engine, run the checks, rebuild after a C++ change, and look inside a card while you work.
Architecture
How a card is computed in the code, and which file holds each part.
Add a technique
Every place a new solving technique touches, from the C++ engine to the card, the explanation and the tests.
Add a rule kind
Every place a new line, edge or cell kind touches, from its registry entry to the engine, the drawing, the docs and the tests.
Grader parameters
Every fitted parameter of the grader by name, with its value and where it comes from.