The rules and logic of harmony sprang from people singing together, so singing harmonies in a pop band – perhaps doing Queen, Beach Boys, Four Seasons, Beatles or Bee Gees covers – is a great way to get to grips with it. Or perhaps you could become a member of a choir – they’re springing up everywhere since Gareth Malone’s TV series, and are a perfect way to meet others with similar musical interests. If you don’t like the idea of that, a barber-shop quartet would not only stretch your vocal prowess, but really embed the principles of four-part harmony into your brain, since they usually follow the Soprano, Alto, Tenor, Bass convention. Singing harmony will feed back to your guitar playing, too: knowledge of chords, transcribing etc. So go on… have a go!