The Mel Bay books were almost exclusively "how to play" books for stringed instruments -- mostly guitar. The few books on keyboards, harmonica or percussion were primarily symposiums on the state of the art. The stringed instrument books start with how to tune the instrument and where the notes are on the various strings. The notes are introduced one string at a time, and there is a short written musical passage between each string so the learner can practice the new notes. When the notes are introduced, the name of the note, its position on the instrument and its place on the musical staff are correlated.
The Mel Bay books have frequent small musical passages so the learner can practice new material. The detail of musical notation, such as how time is divided up between the notes and how rhythm is notated, is introduced a little at a time. The music theory is intermixed with practical advice about playing the particular instrument. The books are small and are progressive, so a student can buy and work through only as many as he needs.
Chords and scales are introduced one at a time as needed. Chord names are correlated with the stacked note notation of chords on the musical staff. The major and minor chords are introduced first, then the 7th chords. The more exotic chords are not introduced until the advanced books. The basic major and minor scales are the only ones mentioned until the advanced books. For the advanced player, there are both chord encyclopedias and scale study books intended for use after progressing through all the method books.
Techniques such as arpeggios, legato and staccato are introduced one at a time as the lessons progress. During, and at the end of, each lesson there are short examples of written music so the student can practice the concepts that were presented in the lesson. There are usually longer -- full page -- works every few chapters and at the end of the book to practice all the notes, music theory and techniques presented up to that point.