Watch the The 5-Of Rule online guitar lesson by Ray Nijenhuis from Western Swing Guitar Guidebook

The "5 of rule" is one of if not THE tool to create moving bass lines. One of the things that helped me a lot in understanding Eldon Shamblin's sophisticated chordal style, was realizing that one can place a dominant 7 chord, also known as the 5 chord, before ANY chord. For example, when you're in the key of G, you could interchange G with its 5 chord, D7. The next step would be playing the dominant 7 chord of the dominant 7 chord. This so called secondary dominant resolves to a scale degree other than the tonic. It enables you to smoothly connect the bass notes of chords and their inversions.