Mediant Modulation

Mediant Modulation is a common harmonic concept used by many composers... especially film composers! The principal simply means to move chord strutures of any denomination to and from each other in intervals of major or minor thirds. 

One of the greatest attributes of this approach is that a progression can come to rest on virtually any chord at anytime...  which is why film composers employ it to great extent since cues are often edited extensively in post-production.

Also if a progression is built in consecutive thirds, even when repeating itself... the composer can actually derive multiple progressions from the original one as demonstrated below. There is also always a wonderful amount of common tones and chromatic connections available for background and melodic development.

                                    (Click once on image for full-size)