Watch the Various Chicks - Mid Strings online guitar lesson by Matthieu Brandt from Guitar Lab: Triads and Hendrixian Double Stops
The three triads we're using in this progression are all major and we're focusing on the middle three strings, string four, three and two. The extensions you can add to these triads generally come from the key you're playing in.
By using extensions you'll make your presence clear without being in anybody's way and avoid boring parts. Extending the three major triads will also get you the three possible minor triads from the same key.