The best song to practise harmony on is one whose tune you already know so well that it takes no attention, and whose line moves by step rather than by leap, because a leap in the tune is a leap in your harmony. Nursery tunes, carols and hymns are perfect for this, which is why every choir warms up on them, and they have the advantage of being public domain, so a practice track of one is not a copyright problem.

Start here

• Hot Cross Buns and Mary Had a Little Lamb: three or four notes, all by step. A third above these is the first harmony most people ever hold.
• Twinkle, Twinkle: one leap at the start, then steps. The classic first duet.
• Silent Night and Amazing Grace: slow, with long notes, which is where you find out whether you go flat.
• Scarborough Fair and Drunken Sailor: minor and modal tunes, once major feels easy. The harmony a third above a dorian tune is its own colour.
• Are You Sleeping and Row Your Boat: rounds, so the harmony is the tune itself, entered later. The easiest way to sing two parts with one tune in your head.

With the harmony written out

Every song above, and forty more, is in Blend's songbook with a second voice a third above and a sixth below, playable and soloable, and the same clip comes up in the lessons that teach its interval, where your microphone grades it.