This guide talks about how to visualize the fretboard, playing on any string, in any position, and in any key.
By associating the note-name to the fret, for every fret (until the 12th fret), you'll 'see' the notes 'light up' for all positions & all keys.
These exercises come from a Canadian guitarist named Ralf Buschmeyer. They require that you: (1) sing/speak the note names as you play the notes, (2) do this while playing in-time with a metronome, (3) with your eyes closed.
They cover 4 common/basic routes for moving & thinking about the neck:
Each chapter/key-centre is like a 'level'; if you finish the C-major exercises, it's like reaching "Level 1 of fretboard memorization". Buschmeyer mentions that by learning these exercises in 4 keys, spaced minor-3rds apart, it covers enough ground to then be able to do all these in all 12 keys.