As we learn guitar notes, we can consider the open strings as points of reference. Once we know the framework we can fill in the gaps with fretted tones.
Try saying each string name and information about the note head location, while playing the open string. As the string is articulated, such as the Low E string, say 'this is string E, the lowest string, it is written as a note head in the minus four space, the space beneath the 3rd ledger line beneath the staff. It has 3 flat hats.' We see the note-head location in our minds.