The first part, consisting of exercises 1 - 20, is labeled "preparatory exercises". These are also the most famous exercises.
Notes by C. L. Hanon :
Preparatory exercises for the Acquirement of Agility, Independence, Strength and Perfect Evenness in the Fingers.
For studying the 20 exercises, begin with the metronome set at 60, gradually increasing the speed up to 108. Lift the fingers high and with precision, playing each note very distinctly.
Observe that, throughout the exercises, both hands are continually executing the same difficulties; in this way the left hand becomes as skilful as the right. Besides, the difficulties executed by the left hand in ascending, are exactly copied by the same fingers of the right hand in descending; this new style of exercise will cause the hands to acquire perfect equality.
Hanon Educational Materials