The easiest to play harmonics are at the 5th, 7th and 12th frets of each string.

The harmonics on the 5th and 12th frets are the same note as the open string (ie. the harmonic on the 5th fret of the D string is a D note).
The harmonics on the 7th frets are the note that the fretted note would be (ie, the harmonic on the 7th fret of the E string is a B note)