when I needed to memorize it for an exam, I made myself some cards - 1 for each fret listing the notes... I probably had it down after a month at 10 minutes a day...

There's also a computer game called 'Fretboard Warrior' which is free to play online here and theres 'advanced fretboard trainer' which isn't free but has more features.

My students seem to like the computer game angle. Using the octave method to find the notes is fine, but it does slow you down. Depends if that matters to you....