If you want to learn the fretboard as in what note correspond to which fret, one way you can start is buy hard memorisng the 6th sting (which means you will also know the 1st string) and identify and play the same notes, say for example, all the C's, on every string. Soon, your knowledge of the fret board will increase. But still, the keyword here is practise.
I'm also trying this method and now i'm qutie good at notes on the 1st, 4th, 5th and 6th strings. Gonna nail the 2nd and 3rd stings after As.
It would really help if you had a chart of the notes on fretboards. Even when you don't have a guitar with you, you can train just by thinking about it. My guitar ensemble instructor teached us this method and i think it works very well.