Watch the The V-IV-I Key of G online guitar lesson by Ravi from Guitar Lab: 30 Rock & Pop Progressions
Certain instruments allow for more interesting opportunities within particular keys. As you have probably realized by now, the key of G is very guitar friendly. The layout of the notes on the fretboard allows our fingers to easily create some very rich sounding chords, and when implemented in a V-IV-I progression, offer a truly signature guitar sound. You have heard it in many songs. It should also be noted, however, that these exact chords can be played in a different order to create a very guitar centric I-IV-V. In the key of G, substitute the C chord with a Cadd9. This allows your third finger to stay down throughout the progression if you use the rock G, giving much more continuity in the sound. Experiment with the D, Cadd9, and G rock chord, it is ear candy for every guitar player, and easy on the fingers too! Try picking the individual notes as well as groovin' and strummin'.
Examples: Sweet Home Alabama, More Than A Feeling, Sweet Child of Mine