I would start with what I call the musical clock which is the 12 notes in a full octave rolled into a circle to replicate a clock (also with 12 points for each of the hours) This makes it easier to picture.
Starting at the top with A can work our way around the clock with the musical alphabet for which I use this rhyme.
The Musical Alphabet is A to G and Everything has a Sharp (#) except B and E
So if you can now picture that clock and start from the Top (A) then the A String on the Guitar is the note of A (Obvious I Know), the 1st fret will be A#, the 2nd Fret B, and so on (see below)
1 A# or Bb
4 C# or Db
6 D# or Eb
9 F# or Gb
11 G# or Ab
So, reading through this is reading the musical alphabet as above
Once you know the musical alphabet and how it translates to the A String you can then transpose this to the other strings so for the E String (which will count for Thin E and Thick E
2 F# or Gb
4 G# or Ab
6 A# or Bb
9 C# or Db
11 D# or Eb
And for the D String
1 D# or Eb
4 F# or Gb and so on
For the G String
1 G# or Ab
3 A# or Bb
4 B and so on
And for the B String
2 C# or Db
4 D# or Eb
5 E and so on
And will will observe, every Sharp (#) has an equivalent Flat (b) as it is 1 semitone (Fret) higher than the note below it but 1 semitone (Fret) lower than the note we are going up to. Also think of this like 12:30pm or 30 Mins to 1pm Its the same but two different ways of saying it.
Learning this will make it easier to find the notes on the guitar quicker plus you can then use other references like.
The 12th Fret is the same note (but 1 Octave higher) than the Open string so the 13th Fret is the same note (but 1 Octave higher) than the 1st fret of the same string. This allows you to quickly learn the notes of the strings beyond the 12 Fret.
Another note relationship worth learning is Octaves so on the lowest 4 strings (Thick E, A, D, G) if you finger a Fret on the Thick E or A String and find that note with the Rhyme(Clock) above then 2 Frets and 2 Strings Higher is the same note (but 1 Octave Higher) If you are on the D or G String you can reverse this to find the same note 2 Frets and 2 Strings Down (but 1 Octave Lower)
When It comes to the top 4 Strings (D, G, B, Thin E) then the relationship is slightly different so 3 Frets Higher and 2 Strings Higher.
As you gain more familiarity with the notes on the neck you will find other relationship patterns but this should get you thinking.
There is a lot to take in so take 1 paragraph and step at a time. Do this with the first couple of examples and the rest will start to fall into place.
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