When I was first figuring out the low B I just mirrored the scale that I knew on the high B. Easy and effective, especially if improvising.
EDIT: I used to try to memorize all different scales all over the fretboard, but for me, I found it was a waste of time. Now, I know the major/relative minor extremely well (not just the pattern, but I learned to memorize every interval value for every note), and I modify it for other scales.
Ex. Harmonic minor. Play natural minor with a b7. Pentatonics, ignore 2 and 6. Blues, add a b5/#4.
Also, getting really good at seeing intervals makes it so you don't have to totally memorize scales, especially for symmetric scales such as whole tone and half-whole/whole-half diminished.
I had a friend that had the "Guitar Grimour" book that is pretty much every scale in every key on the guitar, and I found this to be overwhelming and vastly inefficient. Instead, learning how to modify the major/natural minor to accomplish any mode, or using interval theory to instantly know any symmetric scale really pushed my playing to the next level.
However, this is my personal experience, and as always, YMMV.