I invented this method for tuning a guitar. It never lets me down. You can borrow it too!

You'll need an A note. I use a tuning fork but anything else will do.

Step 1: Tune the D string 7th fret harmonic to your A note.

The D string is now in tune. Now you use the D string for all other strings.

Step 2: Tune the G string to the D string 5th fret.

Step 3: Tune the B string to the D string 9th fret (B).

Step 4: Tune the top E string to the D string 14th fret (E).

Step 5: Tune the A string 12th fret harmonic to the D string 7th fret (A).

Step 6: Tune the bottom E string to the D string 2nd fret (octave E).

(You can test and/or fine tune that by tuning the bottom E 12th fret harmonic to the A string 7th fret harmonic (E).)

Now play a chord, say C or G. If you've done it right it'll be in lovely tune! Some guitars need a bit of readjustment but it should be fine.

It sounds more complicated than it really is. I find it works much better than a tuner.