I STARTED PLAYING THE PIANO IN PUBS at the age of 16. People would ask for a well-known song, and I couldn’t admit I didn’t know it – so I spent a few weeks trying to play songs I knew well enough to whistle, and learning how to fit the chords to them.
Of course, people rarely want to sing in the key in which you’re playing. It took several months for me to learn how to transpose songs on the fly into a variety of different keys, to suit the voice.
People who aren’t able to play by ear think there’s some magic to it, or that you need to be born with some special skill. I call this attitude pianist envy. In fact there’s no magic, and I wasn’t born with it. All it takes is practice.
Start with a simple piece of music. Good starting points are Happy Birthday, or the choral theme from Beethoven’s 9th Symphony, or Good King Wenceslas. Pick out the tune; you’ll hear when you’ve got it right. Assuming you have a rudimentary knowledge of music theory, you can then try to fit chords to the tune – see Six Chord Trick for a tune that incorporates almost all the chords you’ll ever need.