"...and now back to 'Chord Progressions' where we last left them..."
Putting chords together isn't really enough. You also need some good harmonic rhythm, which is how long a chord will last within your progression Here's an example of poor harmonic rhythm:
Because this is such an unusual rhythmic pattern, we can rearrange the pattern to give us something like this, which works a lot better:
Most short progressions will be 4, 8, 12 or 16 bars long. Here is an 8 bar progression which uses good harmonic rhythm, bass movement and basic substitution:
In part 5, we will be going over Secondary Dominants.