Muscle memory. You have probably heard it referred to if you have taken any music lessons or had to do anything repetitive with your hands or feet. I have certainly heard of it through the years but only recently have I come to appreciate it.
Muscle memory comes from repeating some action so many times that you can do it without thinking about it. You can easily see how this applies to practicing your craft, trade, art, instrument, dance steps, etc.
You repeat the action so many times that you can do it without any conscious effort. With regard to scales on your instrument this is exactly what you want.
Take any scale that appeals to you, or any mode (the modes are eight notes in a row on the piano without using the black keys. If you start on c, you end up on c an octave higher. This is the familiar major scale in western music.
If you start on d you end up an octave higher on d, but the intervals between the notes have shifted slightly.
For those of you who don’t know, in a major scale c to d is a whole step, d to e is a whole step and e to f is a half step. They delineate the distance from one note to the other by steps, i.e. c to c # is a half step, c to d is a whole step and so on.
So when you start on d, the second note is an e, a whole step from d, then the next note in the scale is an e, once again a whole step, but now things shift, because the next note is not a whole step a way (like in the key of c: c, d, e, f, g, a, b, c the half steps being between e and f and b and c. between the 3rd and 4th and 7th and 8th notes of the major scale.
Starting your scale on d (on the white keys of the piano) you will find that the half step is not between the third and fourth note in the scale, but between the third and fourth note. The e to f.
If you want to see how the modes work, first play c to c using only the white keys. Now do it with d to d and so on until you have gone thru all eight white notes and you are starting on c again.
Listen to each scale and you will hear how the notes relate to each other. Now find them on your instrument, for me, the guitar.
Play those scales on your instrument until you can play them without looking at the fretboard or keyboard and then apply each of the scales to a song you know. You will see that some work and some not so much.
By learning these scales until they are in your muscle memory and by playing them against songs that you know, you will begin to see the efficacy of having these scales in your arsenal of stuff to play.
Learn every one of the scales in the modes and you will have a unique and wonderful way to solo on songs you don’t even know. Now go practice.