Very simple music theory tips talk.
When we dictate a song or are about to make music, the first thing we should know is the key of the song.
If you know that, you can expect the chords which can use easily.
Maybe the first thing we do when we try to play by ear the music or compose the melodies, the Key discrimination of the song. I write easiest way of it.
NO1. Listen the song with playing some tones on the keyboard or piano.
NO2. You will find possible tones and impossible tones.
No3. Among them, you will find 2 possible tone in a raw.
Already only 2 tones are narrowed down as a Key.
The key is right tone of 2 tones in a raw or 4th left tone from right tone.
If you find another possible tones in raw after 3 tones in the right, the Key is right tone of left 2 tones in a raw.
If you find another possible tones in raw after 3 tones in the left, the Key is right tone of left 2 tones in a raw.
Sorry, of course there are many exception, it has to be major or natural minor key, out of moduraiton, without secondary dominant chord…
Even so, especially for music starter, I think this tips help so much.