I won a competition once by writing a pastiche barbershop pieve once, and I knew very little about it. I regarded the essence of it as follows:
Four part harmony, all male.
Put the melody in the second voice down.
The bass(4th voice) stays below the melody, and the first voice(tenor) always stays above the lead. The third voice(baritone) generally stays between the lead and bass, but can go over the lead in the interests of making a good chord. Ignore the voice-leading conventional rules of standard 4-part harmony, concentrate on making nice chords.
Use plenty of chromatic notes, not just the three chord trick.
Have fun.
Let the chords resonate, pause and enjoy them, dont aim at equal temperamnet tuning as used in classical music etc, let each chord hum and resonate fully and naturally.
That's all I know.