David
Scales are scales, just that, it does not mean they are not important, but only if you understand them and the context in which you can apply the notes within them. What I mean by that is if a piece of music is in a particular key it will likely contain the I, II, IV and V that fit that scale. I am not going to go into their construction here, but for example chords in that work with the A Major scale are A major(I), B minor(II), C# minor(III), D major(IV), E major(V), F# minor(VI), and G# diminished(VII).
For there derivation have a look at https://www.justinguitar.com/modules/major-scale-theory-key-signatures and https://www.justinguitar.com/guitar-lessons/triad-chord-theory-mt-401 if you subscribe to Justin’s Practical Music Theory, which I would highly recommend.
Most chords can be considered of being made of 3 notes primarily and in some cases have notes added or flattened/sharpened to add tonal flavour. If you took a simple chord progression in A Major that used the I, II, IV & V chords a https://community.justinguitar.com/t/how-do-you-actually-start-learning-scales/410584nd had it playing as a backing track and them played notes from the A major scale under the assumption they would sound good you would find they did not. In fact I would suggest you actually learn the A major scale in position 1, that’s A on 5 the 5th fret of string 6, @HappyCat kindly gave you the patterns to refer to, and then try to play notes over a simple backing track in A Major. I think you would quickly observe that some notes will fit naturally with certain chords, some will compliment the chord, some are not too bad, but some will actually sound pretty awful. This is why I believe many people find it so hard to move to improvising and playing solos over songs, it is another step in the learning curve and can be a difficult one.
Blues progressions which generally use the I, IV and V chords can be a good starting point using the Pentatonic Minor scale. This scale is basically 5 notes that are derived from the Major scale. the thing is that these note generally work well of the I, IV and V chords of the MAJOR Scale, so it makes it easier to make up licks and solos using notes in the Minor Pentatonic Scale. This is a bit of a simplification but a good starting point.
The next step in soloing over songs generally is to do what is called ‘Making the Changes’, this simplistically means using notes from scales that chords can be derived from or Chord Tones, Jazz musicians use this approach a lot, sometime to create harmony and be melodic and at other time to create dissonance. Getting to this point takes time, patience and a good understanding of Music Theory in my humble opinion.
Going back to my point learning scales in isolation is not a good idea, although it will improve co-ordination and dexterity if done properly. I have learnt scales it in the past, and still struggle to use and apply them when improvising. One aspect of learning guitar which I found very helpful was the CAGED system, this method brings together Chords Tones, Scales, Chords and their relationships in a practical and organised way if taught and explained well, and at the same times helps open up the fretboard to the guitarist. Justin does to a course on it https://www.justinguitar.com/modules/caged-system I have never really understood why it is marked as Grade 6 as it is the building blocks, but maybe he considers it a step to far and may be too soon for beginners to take.
You might want to dip you toe in here as well https://www.justinguitar.com/classes/scales-modes
i hope you find my answer helpful.
