The common way to learn scales on your fingerboard is through position patterns. This, however, means you have to memorize as many scale patterns as there are notes in the scale. For example, the major scale has 7 notes, and there are 7 positions of the major scale. So only to cover major, harmonic and melodic minor scales you have to memorize 21 patterns. And it doesn't get any easier if you go on to learn the "exotic" scales.
3-note per string scales are a little easier - for example, in order to play the major scale:
there are only three 3-note patterns you have to learn:
5-6 of these little patterns will cover most of your scale needs; however you still need to know how to combine them.
So now on to the ultimate laziness in the guitar world: 4+3 scales. I actually picked this up a while ago, in a lesson by the guy from Chops From Hell
. Pretty cool site. Enough with credits already :)
Here's the main idea. A seven tone scale has, oddly enough, seven tones. So it's enough to memorize one pattern of these seven tones and repeat it in octaves. Below is a harmonic minor pattern. You can clearly see a seven note pattern repeating on each set of two strings, four on the lower and three on the upper (hence 4+3). The root of the harmonic minor is on the 2nd note of the pattern! You can use any pattern of seven notes, but this one is easiest to finger:
We just spanned nearly three octaves with a single pattern. Pretty cool, huh? It gets better. You can cover the remainder of the fretboard with nearly the same pattern. Think about the 6th string on the pattern above. The pattern itself repeats on the 4th string, but also on the 6th string 12 frets higher. But, there's an empty space there - three notes are missing.
Lo and behold, it's the same three notes that are found on the 5th string. Ofcourse, the pattern repeats on the 5th string 12 frets higher as well, and the notes missing are those found on the 4th string. And so on, this basic 7 note (3+4) pattern repeats itself on every other string. Here it is (root is the 5th note of the pattern):
As you can see, it's merely an inversion of the first pattern. So with these two, we can cover the fretboard in it's entirety.
This approach works for any 7 note scale, although the major scale is a little hard to finger on lower frets. This fingering is the easiest for me (you can work out the other pattern for yourself):
The approach works for scales with more (or even less) than 7 notes as well, but the fingerings can't get pretty awkward. But it's feasible - you can cover 8 note scales with 4+4 patterns, 6 note scales with 3+3 etc. I'm sure you're all familiar with these two:
Ofcourse, the "other" patterns of the scales above are the same above patterns.
The other advantage of this approach is that you can see the interval relations instantly. In the (Ab) major example above, the 5th (Eb), for instance, will always be the last note of the first pattern and the third note of the second one.
Lazyness all da way :) Happy picking.