What really helped me was doing one string at a time and saying the note names to myself as I went up the fretboard one step at a time.
Another thing that helped was taking a diagram of the fretboard and writing the notes out on that so that I could see the fretboard. Doing this was an activity that pushed me to memorize the notes.
Visualizing is the next step where you can see the fretboard without actually playing the guitar and know what the notes are.
You can check out this article about some visual techniques.

http://www.shredaholic.com/fretboard-visualisation.html

Thanks,
Joe Pinnavaia
http://www.joepinnavaia.weebly.com