Usual approach is first major then minor. I had got quite used to minor blues in Bb and realised the relative major comes by ignoring the 5b , adding the 2 ie C and the 6b ie F#. Bingo I now have all the notes of Db major. Obvious I suppose but it came as a revelation to me. Familiar with the blues then the major scale on the flat third is but 2 notes away.
whatever works for an individual is great. go with it.
but that does seems quite a complicated way to think of it.
i think eventually we are all aiming to have the notes of any chord/scale under our fingers in an instant, without having to work through any complicated methods to arrive at that.
for me, keeping it simple in practice is the best way. I like to play major and then relate stuff to that, one after the other. this applies to scales and/or chords.
So, for example, play the major scale, then a minor scale on same root then the blues scale.
so, the root stays the same. this is important. It gets you thinking in that key rather than from other keys transfered. I like to think of what notes are changing from major in that key
so C major: c d e f g a b c
C melodic minor : c d Eb f g a b c ( or, you could use the Dorian instead : C D Eb F G A Bb C )
C Blues : c Eb f, f sharp , g, Bb c
You could continue to add as many scale types as you wanted. I wouldnt suggest that in early stages. those 3 are more than enough to get your brain, fingers and theory together
For me, thinking of the C blues as being from the complete ( ie whole thing )Eb major scale is a bit too complicated.
However, it can be useful to think of the blues scale as being derived from the major pentatonic of the flat 3rd of that key, with only one added note. Keys of C and Eb in this example.
( that sounds complicated. It isnt. re -read it and digest. )
So, we are looking for C blues scale.
Go up a minor 3rd to Eb. Play the Eb major pentatonic scale : Eb, F, G, Bb, C, Eb
Now add one extra note. The F sharp. ( this is the flat 5 of C... the blue note !! )
Eb, F F sharp G Bb C Eb.
Now use those notes, but starting on C
Hey presto. C blues scale.
Go with what suits you best, but this works for many.
good luck
EDIT. ive just remembered something.
I was at an IAIN BALLAMY workshop 2 days ago.
He said that he basically just thinks 2 scales. Major and Melodic minor.
He goes up and down the major, then the same root melodic minor.
then he goes up a half step and does the same. then up another half step etc etc.
12 roots.........., 24 scales
he does add different articulations in, to give himself more permutations, but basically , that is it.
