They are many ways to practise scales. My favourite method is as follows. I set the metronome at a nice comfortable speed, 60 to the quarter note. I play the scale in quarters, then eighths, then triplets (for a two octave scale play the scale 3x in a row so that you end up on the downbeat), then sixteenths.
To work up the speed from this point, I start at a speed that feels comfortable or even too easy, when I can play it 3x without error (if I can't play it 3x without error, I pick a lower speed), then I raise the metronome 12 beats per minute (for example 60 moves up to 72), play it once, then I move the metronome down 8 beats per minute, play it 3x, up 12 1x etc.
This is an amazing technique that was introduced to me by my husband who read about it from an article written by a well- known clarinet player.
By constantly changing the tempo faster and slower you challenge your nervous system to ''be on the ball''. It improves your technique and your mental clarity. Perfect one scale before going on to the next. You don't have to have it learned up to speed but learn it well with good technique.
With piano, the fingerings for most scales are the same. You have a default fingering for most scales starting on white keys and a default for most scales starting on the black keys and then are the exceptions. Learning one well will help you learn the next one more easily.
Lastly, two more things: 1)Always, always, play your scales musically. After all they are music. A D major scale played in reverse is the beginning of ''Joy to the World''. Playing musically makes practising scales enjoyable. 2) Make sure that your hands are always relaxed and comfortable. Resist the temptation to play faster if you cannot do it without getting tense. This will prevent you from getting into bad habits and prevent injuries.