A strong melody will be easier to learn to play by ear.  Rock or folk songs usually have strong, easy to recognize melodies. Avoid songs with inconsistent melodies, such as rap and hip hop tracks. In music, notes combine in a specific way to make a scale or chord, and chords come together to form chord progressions. Chord progression patterns are especially common in popular music, so you should be able to recognize common patterns when you hear them.  Recognizing chord progression patterns will help you to anticipate chord changes as you listen to a piece of music. For example, popular songs like ‘La Bamba’ and ‘Twist and Shout’ share one of the most common chord progressions of all time. If you can play the chords for one of these songs, you can easily play other songs with the same or similar chord progression. This will help you find the key of the song.  To find the key of the song, you must first find the tonic or the root note, which is the first and last note in the scale of the song.  For example, in the key of C Major, the tonic is C. The notes in a scale or key are like a family, so they are related and center around the tonic of the key. The tonic or the root note of the song will be the tone that sounds the most ‘at home’ in the song. It will sound like it could fit just about anywhere in the song. Now that you’ve found the key of the song, try to find the melody based on the notes in the key. For example, in the key of C, the notes are C,D,E,F,G,A,B,C, so the melody will fall within these notes. In general, the notes of scales and chords are assigned specific numbers. So, the fifth is a fifth note of the scale.  If we use ‘La Bamba’ as an example, it is in the key of C major. So, G is the fifth degree of C Major, as you go five degrees up from C Major, i.e. C,D,E,F,G, A,B,C.  It’s best to play a fifth above the tonic as the fifth is always the second most stable tone in any key. This tone should also feel like it could belong in any part of the song, though not as strongly as the tonic. Focus on finding the root note for each of the chords, and then determine the fifth.  For example, the root of the next chord in ‘La Bamba’ is F. To determine the fifth of the F chord, count five degrees up from F and this gives us C, i.e. C, D,E,F,G,A,B,C.  Continue the same process for the next chord. Focus on playing each chord in sequence along with a recording of the song. This will help you determine if you are playing the right chords. If a chord sounds off, go back and try to adjust it based on your ear.
Select a melodic song. Listen closely for patterns in the song. Play the notes in the song one-by-one and observe how they sound. Determine the melody of the song. Play a tone a fifth above the tonic to determine the chord progression of the song. Repeat this process for each chord change.