Hi Bob,
I have a few ideas
First, paint for your porfolio. Seek out subjects not yet represented (eg, ages, gender, ethnicity, doubles, triples, whatever) and paint them in the way you would like to paint .That may or may not be consistent with what wil sell. Include both, if you feel they are different.
Second, start a folder of techniques you'd like to try and portraits you wish you had painted.Try them.
Third, go to every open studio group you can, or start one, even if you are the only artist.
I guess I could fill up about ten years with that stuff - good luck