Music is fascinating, isn’t it? Today I made the following progression to illustrate how dominant chords work. Any time you want to change keys you should play a new dominant seventh chord to state the fact that you are in the new key.
This example has every secondary dominant in the key of G Major. The closely related keys to G Major are: A Minor, B Minor, C Major, D Major, and E Minor. You just need to add the dominant chord of each of those keys prior to playing them. (I added F Major because I am a rebel.)