First of all congratulation for shortlisted in Medical Officer Interview in UPPSC and here are some useful tips for preparation in exam:

Do not show relaxed attitude during the interview.
Do not forget to take the relevant documents along with you to the interview venue.
Prepare some questions about the organization, on GK and about the stream also.
Do not remain silent or uncommunicative during the interview.
On that day the candidates must get to on before time at the place of the interview.
Candidates must dress in a very conventional and smart manner.
Do not forget to acknowledge persons in the interview Board.
At the end of the interview, say thanks the interviewers for their time.
Be confident but do not show over confidence or unnecessary attitude.
Candidates must be relax and calm themselves before and during the interview.
Do not smoke or chew gum before and throughout the interview.