Theory can be a tad boring, but it's important. Just getting started, getting your feet wet in it can help loads. For instance: just learning about keys and scales helps out a lot. Also some consonance and dissonance are good things to get familiar with.

You guys know a few chords, and a lot of them can be used together, but if you also learn a bit about consonance and dissonance that can really add to your playing emotionally by creating tension and alleviation in your music. Learning not just HOW to use chords together, but WHY they sound good together opens up your ability to apply this knowledge to other chords and keys.

None of these things take a whole lot of effort to learn the basics of, but when you start getting into it, it should help the rest of the process knowing that you have actually learned something applicable. However, truly controlling consonance and dissonance is something I have yet to do myself as it requires much much practice and experience. The basics are as simple as throwing a minor chord in a major chord progression.