Learn the notes on the E string, then the concept of an octave and how to find them.

If you play the open E string, the octave for this is on the D string 2nd fret.

The easiest way I found was to think of the notes on each of the strings are a repeated pattern starting in different positions.

Start with the whole notes (no sharps or flats)

EFGABCD ABCDEFG

Once you've got them down you can learn the sharps/flats