A doctor/nurse/health-worker take following precautions to avoid become sick themselves
(i) Wear masks while diagnosing mouth or chest infections.
(ii) Clean their hands and wear gloves even while doing minor surgeries.
(iii) Get immunisation done against all the infectious diseases.
(iv) Take balanced diet (rich in proteins especially) to strengthen their immune system.
(v) Dispose off blood samples, urine or stool, sputum, etc., carefully.