Whether you are going to play chords, scales, solos, or otherwise improvising, it will generally give you many benefits to know all the notes on the fingerboard.
If you set yourself small goals and learn one string at a time, you will learn all notes on the fretboard in no time!
The musical alphabet
There are only seven natural tones in the musical alphabet: A B C D E F G (the first seven letters of the alphabet). The seven tones is repeated, so the natural tone occurring after G is A.
Distances between the tones
First and most important - you need to think in distances between the different tones. If you move one fret up the fretboard, the tone will be raised with a semitone. If you move two frets up the fretboard, the tone will be raised with a whole tone. There is a whole tone (2 frets) between all the natural tones except between E and F as well as B and C, where there is only a semitone between (1 fret).
The string names
The strings are numbered from the thinnest to the thickest. The thin string is number 1, and the thickest is 6. string. Below are the guitar fretboard, with the string number and tone (in standard tuning).
If you do not understand the image above, try to lay the guitar on your lap with the strings facing up. Now the thickest string is closest your body and the guitar now looks like the diagram.
The natural tones (string 6 and 5)
The 6th string is named E. Between E and F there is a semitone (1 fret), so F is located on the 1st fret. Between F and G there is a whole tole (2 frets), so G is located on the 3rd. fret. Between G and A there is a whole tole (2 frets), so A is located on the 5th. fret. Try to find the rest of the natural tones on 6th string up to the 12th fret. On the 12th fret the musical alphabet starts over again, so the 12th fret is an E.
Here is a diagram with the natural notes on 6th and 5th string up to 12th fret.
Start practicing all the natural tones on 6th string and thereafter continue to the 5th string. Say tone name loud while playing until you can all the notes by heart.
You should review this process on all 6 strings, but do your best to learn the 6th and 5th string first. All scales and chords has their keynote placed on these 2 strings, and you will soon discover that it all suddenly hangs together in a greater whole.
The natural tones (string 1-4)
You can now find all the natural tones on the fingerboard. The next step is to learn the rest of the notes. So we have to fill in the gaps.
Accidentals (sharps and flats)
# After a tone means that the tone is a semitone higher. b after a tone means that the tone is a semitone deeper. F# and Gb are all exactly the same tone. There are just more ways to think about the tone. It is in fact the key and the situation that determines what we should call it. Learn now the notes on the fretboard. When you can count your way to all the tones you come very far.