I had a left nephrectomy for renal cell cancer t1b tumor. Is there anything I shd be doing to protect the health of my r kidney besides 6mo testing?

Protective measures. Glad you got surgery in time, you can take various protective measures, if some gets chronic renal disease by any reason, out come will be the same with one kidney or having two, first control, BP & wt regular exercises , drink plenty fluids control diabetes ( blood sugar ), avoiding IV contrast tests, angiotensin, &arb agents found to be useful in protecting kidney(s).
Keep well-hydrated. Keep well-hydrated. You should drink enough water each day so that your urine is always a pale yellow color. Maintain a healthy body weight and avoid diabetes. If you have high blood pressure, make sure it is very well controlled. Check with your doctor before taking any new prescriptions. Check with your doctor before getting IV contrast for ct or MRI scans. Your right kidney will be happy!