Fundamental to excellent ear-training (read: brain-training) is a system for understanding the relationship of a note in the key. There are several popular systems: numbers, movable-do solfège, and fixed-do solfège are among the most common.

Solfège scales can be a tremendously helpful practice and should be completed regularly in as many tonalities as possible.

Bonus: Mastery of scales is essential for vocal runs in contemporary commercial music.