Tuning one string changes the pull on the neck, so the others can shift slightly. A second pass fixes that.
With an electronic tuner:
- Set the tuner to standard, A = 440 Hz.
- Pluck the 6th string (low E) and tune to E.
- Repeat for A, D, G, B and the high E.
- If you overshoot, go below the note and come back up. That keeps slack out of the tuner gear and string.
- Check all six again.
Without a tuner, once the low E is in tune you can tune by ear:
- Fret the 6th string at the 5th fret to get A, and match the open 5th string.
- 5th string, 5th fret matches open D.
- 4th string, 5th fret matches open G.
- 3rd string, 4th fret matches open B.
- 2nd string, 5th fret matches the open high E.
New strings stretch and will drift flat for a while, so expect to retune often during the first few sessions.