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.