Understand the rules before you drill the questions.
The official catalogue has about a thousand questions and every app sells you the same thousand. Vorfahrt is the part that comes first: the rules themselves, made small enough to hold, so that when you open the question bank you are revising rather than meeting each rule for the first time.
Right of way9 models
One strict ladder decides almost every junction. Work a crossing and watch which rung resolved it.
The sign system6 modelsShape and colour carry the category. A sign you have never seen still tells you what kind of instruction it is.
Distances and numbers3 modelsThe un-guessable half, and where the heavy questions live.