How to Play Natural Harmonics on Electric Guitar

Performance:

Instead of pressing a string between the metal strips against the fretboard as when playing regular notes, softly touch it right above the metal strip, the one of the two which is located closer to the bridge, and stroke the string with the picking hand as usual.

After the stroking, immediately take off the finger of the fretting hand out of the string. And you should get a bell like sound:

Playing Natural Harmonics - Fretting Hand
 
The spots on the fingerboard where it is easiest to get natural harmonics are over the 4th, 5th, 7th, 12th, 16th, and 24th fret:
Locations on the guitar fingerboard where it is the easiest to play natural harmonics

Most natural harmonics have higher pitch than a "plain" note played at the same fret:

Natural Harmonic at Actual Pitch
4th fret 2 octaves higher
5th fret 2 octaves higher
7th fret 1 octave higher
12th fret the same pitch as with a plain note
16th fret 1 octave higher
24th fret the same pitch as with a plain note

Here is a little lick to practice natural harmonics:

A melodic exercise to practice playing natural harmonics - guitar tablature

In printed guitar tabs natural harmonics notated as:

Natural harmonics notation used in guitar tablatures

In plain text guitar tabs it is marked as a note between the square brackets:

1|----------------
2|----------------
3|-----<12>-------
4|----------------
5|----------------
6|----------------

as well as N.H. characters, or sometimes as a '+' symbol above the lines representing the strings.