1. You don't have to tune the low E string. When you tune your guitar to itself, it will sound good, even if it's not in tune with the rest of the world.
2. Fret and play the low E string on the 5th fret. This sounds the note A, and gives you a reference to tune your open A string to.
3. The A string on the 5th fret will give you a reference to tune the open D.
4. The D string on the 5th fret will give you a reference to tune the open G.
5. The G string on the **4th** fret will give you a reference to tune the open B.
6. The B string on the 5th fret will give you a reference to tune the high E string.