Another method of ear training is to go through the scales and focus on singing the notes of the scale in perfect pitch. Start with just one scale and sing the notes as you play them. Gradually work on singing the notes whilst playing them less until you can sing the scales with only playing the root note at the beginning. Repeat the process with other keys.

This may not be the best method for everyone. Its essential to keep laying and practicing as you do, and eventually your ear will be able to identify simple chord changes and melodies over time, as well as the sound of a guitar in perfect standard tuning.