Step 1) Play the Tonic pitch for the given chord progression.
Step 2) Sing the bass line only, from beginning to end.
Step 3) Sing each chord one at a time on scale degrees, ascending then descending, finding the next bass note before continuing to the next chord. Be sure you sing on the same pitch any common tones that may carry over from one chord to the next. If necessary, play the next bass note before singing each chord (see example).
Step 4) Pick a new Tonic pitch and repeat steps 2 and 3.