By learning to play the following progressions in all keys using inversions close together on keyboard or guitar, you will develop good voice–leading habits and will also be well prepared for harmonizing most major key melodies. Learn to play the progressions from memory using either hand while playing the root note of each chord with the other hand.
Here is a Chorale in the key of A major, written by the all-time master of voice leading – Johann Sebastian Bach. Listen to the majestic sound he creates with just four human voices. If you are serious about learning harmony, it is recommended that you purchase a book of Bach’s Chorales and study some of them with a Classical harmony teacher. This will improve your ability to write and sing harmonies regardless of the style of music you sing.