Anybody even vaguely familiar with music theory knows that the white keys on a piano make up the C major scale. I like to think of the twelve notes as being mapped out on a clock with Ab at midnight. The C major scale, which is symmetrical around the vertical axis, then read alphabetically clockwise from the top.
Intervals are easily handled with the clock notation. What is three semitones up from Eb? Since Eb is at 7 o'clock it is the note at 10 o'clock which is Gb. We have all practiced adding and subtracting hours every day of our lives so why not use this skill to determine the relationship between the 12 notes in the western music scale? It has the added benefit of an immediate visual appeal that I personally have never managed to perceive in the standard musical notation. Have a good look at the pattern made up by the the white and the black keys on the clock, and the positions of the sharps and the flats should no longer be a mystery to you (in these politically correct times I hesitate to point out that the accidentals outline the shape of a black man). Make it a habit to translate the name of a note to the time on the clock, and vice versa. You can practice this anywhere, anytime. In fact, it is best if you try to visualise the notes on the clock without the guitar in your hands. You will get used to it very quickly.
Let's jump ahead, and look at how the notes on the fretboard are mapped to the clock notation. Here is a good way to think about it. Divide the six strings into two groups: the top three and the bottom three. Both groups are tuned, from low to high, E-Ab-C. On the Ab strings, the 2nd and 5th which are in the center of each group, the fret number is the same as the note in clock notation. On the E strings, the 3rd and 6th which are in the bottom of each group, you get from the fret number to the clock notation by subtracting 4. On the C strings, the 1st and 4th which are at the top of each group you get from the fret number to the clock notation by adding 4. Thus, for a given string you just have to determine whether it is the top or bottom in its group, then add or subtract 4 from the fretnumber. The system is illustrated below, with clock notation on the upper staff and tablature on the lower staff. You can think of the clock notation as being tablature for a guitar with four strings tuned to Ab in increasing octaves (in fact, that is how I produce the clock notation in a tablature editor). Be aware you have to know how to "wrap around noon" as you do in real life. For example 4 hours before 3 is 11 and 4 hours after 9 is 1. Also note that midnight is notated as 12, not 0.
MSG is ideally suited for the M3, and it is described in the Wiki of the Music Notation Project. It is a chromatic system that spans 3 octaves, starting from the open E on the lowest string. As suggested by Schoenberg staff lines are separated by 4 semitones. Credit goes to Paul Morris from the Music Notation Project for providing a MSG template for Lilypond, the typesetting software I use to generate the beautiful sheet music on this site.