Here's how I've remembered how suspended chords work. Whatever string is playing the root note of the chord, the next higher pitched string is playing the third of the chord. Play a D major on the three highest strings, and the note on the high E string, F#, is the third. To suspend a 4th, play the high E one fret higher (the G). To suspend a second, play the F# two frets lower (open E).

If you're playing a first position A chord, the A is on the G string, and the third (C#) is on the B string. One fret up from C# is D, the suspended 4th, two frets down is the open B, or suspended 2nd.

On an F major in first position, A to Bb on the G string is a suspended 4th. The open G string is the suspended 2nd. Shift the pattern to the next lower pair of strings, and you can do the same trick on the C major chord, and another pair and you can to the same thing for the first position G chord.

You can also voice the chords differently by playing the suspended notes higher in the chord. In the song "Darling Be Home Soon", there's a C suspended 4th, major, then suspended 2nd riff played on the D string, but on other songs, C sus4 sounds better voiced with the F on the high E string.

The Who's Pinball Wizard uses suspended 4th barre chords, where you shift from using the "A" form barre chord with the fingers shifted one set of strings lower, then an "E" form barre chord on the same fret when it moves to the major chord.

Suspended 4th seem to be extremely popular with a lot of old school songwriters, like Dylan, Tom Petty, and Sonny Bono.