Here is some info from the Melody To Chord Guide lesson in the 'Convert Songs to DecPlay' course

Top Tips for Adding Chords To A Melody

Most songs just use the 6 standard chords (1 to 6) and many songs start and end the song on chord 1, as this is what audiences are used to and it feels like the song comes to a 'conclusion' when it ends on chord 1. 
The attached chart shows which standard chords go best with which melody note.
If you are playing a famous song, you can also get the chords online for most popular songs using the free services at - I recommend using chords in the key of C major (most common chords being 1 4 5 6 ie C F G Am). If the song is in a different key, you can use the transpose buttons to chance the key.