It may sound boring, but when you've done it, it opens so many doors. . . you can spot and play chords in positions you never thought of, you can play licks all over the neck without having to spend time figuring out different positions, you can start to READ MUSIC!!
Take it a few frets at a time, and be patient. Soon you'll know your fretboard notes like you know your open strings.
Try "Fretboard Warrior" - it's a small downoaded program which tests your knowledge. Do it once or twice a week and keep track of you score. I used to have weekly contests with my mates!! I usually lost but it adds incentive!