If you want to spice things up from the chart below, you can occasionally play the 3rd as the root. This usually occurs when following after a full measure of the same chord eg measure 2, and would be written as D/F#. The D7 in measure 10 sounds like it has the 5th (an A) in the bass, and I also hear an E, or sus2 in there as well. The A7 has the 7th as the bass as a leading tone to the F# note (as the 3rd of the D chord again in the following measure).
