What was previously mentioned, and what I do a lot at work is drawing my own fretboard diagrams. Just draw 6 lines across for the strings, and then 12 or more lines cutting across those lines for the frets (hint: the same notes & patterns repeat from the 12th fret onward). You could do one diagram with all the notes first, but I prefer to map out things like all the G notes or all the notes of a certain chord or scale. Doing this will reveal many patterns that occur on the fretboard. And believe me, the guitar fretboard is all about patterns, so if you discover those, you'll never get lost.