I have been on a vacation in Czech Republic, and have been on several campings. On one of these campings was a professional music theory teacher who had lessons on a University School of Music, and is now a music theory teacher at a Gymnasium.
He taught me about the Circle of Fifths, especially how to create it from scratch. I had to write down all the scales in the circle of fifths, and he wants me to completely memorize the Circle of Fifths, and all sharps and flats in the twelve keys. He also taught me about I, IV, and V, and how to get those chords out of every scale.