Start by humming, not playing

Every good ear player begins away from the keyboard. Before you touch a key, hum a tune you have known for years — Happy Birthday, Twinkle, Twinkle, Little Star or Auld Lang Syne. Hum it until it is steady and you can repeat it exactly the same way twice. Notice the shape as you go: does it climb, fall, or sit on one note? Most people can sing a tune accurately long before they can name a single note, and that accuracy is the raw material we are going to work with.

One piece of housekeeping first. If your piano has drifted badly out of tune, your ear will fight you all the way, because a fifth that should sound sweet will sound sour instead. A piano in regular use wants an annual tuning, and more often if it lives beside a radiator or a window that catches the sun. Get that sorted and everything below becomes far easier.

Find your first note on the keyboard

Sing the first note of your tune and hold it on a comfortable "la". Now find it. Use middle C as a landmark and ask yourself whether your note is higher or lower. Then walk the keys one at a time — no leaping about — until the piano matches your hum. When it locks in, you will feel it in your chest; the two sounds fuse into one.

Write that note down. It is your anchor, and every other note will be measured from it.

Work out the melody one interval at a time

Play the second note of your tune. Still humming the phrase in your head, ask three questions in order:

• Is it the same note, higher, or lower?
• If it moves, is it one key away (a semitone) or two keys away (a tone)?
• If it is further, count white keys up from your starting note: landing on the fifth white key gives you a fifth, as in the opening leap of Twinkle, Twinkle.

Most melodies move by step, so tones and semitones will carry you through the bulk of the tune. Treat leaps as landmarks. Work one note at a time, always replaying the note before it so your ear stays anchored. It feels slow at first; within a few weeks the notes start arriving in pairs and threes.

Add bass notes with your left hand

Once the melody runs smoothly in your right hand, add a single left-hand note per bar. Start on the note your tune sits on — if the melody lives around C, begin with a low C. Play it on the first beat only, and let it ring.

Next, try the fifth above that note (from C, count up five white keys to G), alternating root and fifth on the strong beats. Simple, spare and steady beats clever and cluttered every time. You are building a floor for the melody to stand on, not a second melody to compete with it.

Test your chords against the melody

Now the satisfying part. In any major key, three chords will carry the vast majority of tunes you know: the chords built on the first, fourth and fifth notes of the scale. In C major that is C, F and G, with A minor as a very useful fourth option.

Play the melody note and hold it. Then play a chord underneath and listen. The wrong chord will sound cluttered or restless; the right one sits beneath the note like a cushion. Test each chord in turn against that note before moving on. You will soon spot that the last note of a phrase almost always wants the chord built on the first note of the scale.

Keep the left hand light while you do this. If a chord sounds muddy, it is usually because you are playing too many notes too low down, not because your ear has let you down.

A practice routine that actually builds the skill

• Ten minutes daily beats an hour on Sunday. Ear work rewards frequency above all else.
• One tune a week. Hum it, find the first note, work out the melody, add bass, then test chords.
• Sing as you play. If you can sing it, you can hear it; if you can hear it, you can find it.
• Revisit old tunes from memory after a fortnight and notice what your ear hands you unasked.
• Keep the instrument healthy. Sticking keys, a squeaky pedal or a piano that has slipped a quarter-tone flat all make listening harder than it needs to be.

Playing by ear is not a gift handed out at birth. It is a habit of listening closely and moving slowly, and every pianist in your street who makes it look effortless has simply done more of it than you have. Start with the tune you hum in the kitchen, and the rest follows.