Simply put the guide tones are the 3rd and 7th of any chord. These two notes contain the essence of the chord. All chord’s can be reduced to these notes and still retain their harmonic function. Keep in mind that 9th’s, 11th’s and 13th’s (and their variations) are chord extensions which add color to the chord, but do not effect the chord quality.
Often pianists and guitarist’s will use guide tones in comping for others or themselves. In addition if you analyze any of the great players in jazz you will always find guide tones present in their solo’s.
Using the guide tones within a solo is an excellent way to help propel your solo forward and give it a real sense of movement. In fact J.S. Bach used guide tones to great effect in his unaccompanied music for violin and cello. Even though there is no harmonic accompaniment in these works the strength of the melodic writing and the use of guide tones outlines implied harmonies and creates harmonic movement via the melody.
1) To help your understanding of guide tones pick a solo from a player such as Charlie Parker and analyze his solo. Then select one of Bach’s unaccompanied pieces for violin and compare how the guide tones are used in each (I would recommend also playing the solo and singing it).
2) Next, begin to implement guide tones into your playing. You can begin by playing one or both guide tones per measure in a 12 bar blues and then go on to some of your favorite tunes.
1) An excellent way to improve your ear is to play the guide tones at the piano and sing the root of the chords through a progression such as a blues. Or any progression from any tune. However, I would start with the blues.
2) Next begin to work on playing the root and singing the guide tones in a arpeggiated fashion. If you do this daily you will find that your ability to hear the inner-workings of a tune and to aurally navigate them will become much more fluid. In addition your musical confidence will increase.
3) A more advanced kind of ear training is to play the guide tones at the piano and sing lines over them. Do this and all exercises through all the keys.