Step 1. Learn the chromatic scale. The chromatic scale consists of 12 notes. *A, A#, B, C, C#, D, D#, E, F, F#, G, G#. To better understand the chromatic scale I recommend you check out the G4 Guitar Theory book. To receive a free copy subscribe via our website www.g4guitarmethod.com .
Step 2. Find all the A notes on each string and memorise their positions. Practice this for a week.
Step 3. In the next week find all the B notes and practice everyday for a week. 3rd week find all the C notes and so on.
The idea is to rotate around the notes spending a week on each until you can find any note instantly then use the chromatic scale to locate the sharps and flats.