what exactley is the proper way to play scales once you know the construction for say, a C major, and you know all the notes on the fretboard.

do you play only one or two octaves?

ascending up the entire neck and descend back down?

is there a 'right' way to do it?
i usually pick three notes then slide to the fourth and move to the next string. Just start at the lowest root and move up. it helps for memorizing where the scale is.

That said, it's insanely boring to practice that way. I like just playing a pedal tone (root) and then making some melody around it using the scale. Thing is, you need to know where it is (part 1 - boring) before you can play around with it (part 2 - interesting).
All you have to worry about is getting the right notes and patterns. Other than that, it doesn't really matter how you play them. Though you shouldn't really be going up and down the neck on one string. Wether or not you play 1 or 2 octaves is up to you.
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There is no "proper" way - at the end of the day scales aren't necessarily made to be played, just used for creating more interesting things. If you just want to play scale patterns as a warm up or exercise then you can arrange them however you want.
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