When I was teaching in Topeka, Kansas, I got a call from an older gentleman. He asked me if I teach scales when I teach Guitar. Well, yes, as a matter of fact I have always done that even if I had to disguise them as a tune for the "kids." That's what he wanted to hear-he explained to me that he studied Guitar at the Charlie Parker School of Music in Kansas City, but with winter coming on, he was hoping to find a Guitar teacher locally & he figured if I taught scales I must know how to teach correctly. Charlie Parker, he said, always taught that scales are the basis for all Music.


How I practice depends somewhat upon which instrument. Voice, I vocalize for at least 30-45 minutes before any singing of songs & an hour is much better. (Vocalizing incorporates scales & portions of scales) I vocalize every day unless I have some sort of creepin crud respiratory/throat thing.
Piano, I begin slowly to allow the old arthritis to calm down, with both hands starting toward the left end of the keyboard in the key of C going up slowly then back down. Then, going around the circle of fifths. Then arpeggios.
Brass instrument, I buzz my chops & then in the mouthpiece in arpeggios first, then it's long round tones on the horn for awhile, -maybe longer than other folks as I don't play much these days.
Flutes, I begin with middle tones in whole notes going down, then up. Yeah, scales. Gotta get that embouchure goin'.
Whistles, gee--Irish tunes seem to be full of scales & portions of scales.
Pickin' instruments, I get the old fingers going in one key or another in an upward & downward manner--yeah, I guess that'd be scales. Before I rehearse any given tune, I play scales in that key to get the correct notes "under my fingers."
Autoharp, (mine is tuned chromatically) I get my fingerpicks on & play scales up & down in whatever key so that my fingers remember "where the notes lie on the strings" in that particular key before I play any tune. I often have to try different keys before I decide which key to choose for a given tune.
& similarly for other instruments--I use scales on every instrument (except many percussions) as all my teachers taught. Mr Parker knew what he was doing.