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Tune the first string down to an E. If you are using a piano, play an E note and match the low E string to that note. Take it slow and make sure the notes are synchronized. This can be a good technique if your tuner is not chromatic. Chromatic tuners hit all the notes including sharps and flats. Go through each string either using a tuner, piano, or your ear. Play a standard E chord and check to see if everything sounds tuned. Go through each string within a chord, and make sure it sounds in tune. Rely on your ears, but you might need to use a tool.
Find a tuner or a piano. Tune the rest of the guitar normally. Adjust the tuning.