Make sure you are well familiarized with the company of interest! Check their website, social media, or even a quick google search can help you be prepared for any questions thrown at you during the interview. Plus, knowing the company goes to show that you are actually interested in the position you are applying for!
Before the interview - practice common interview questions and prepare short answers to them. You want your answers to sound rehearsed and polished, but not scripted. For research positions, there is a good chance your interviewer will ask some technical questions regarding your experience with specific techniques. Make sure you are aware of what skills and techniques are recommended, or even required for the position.
During the interview - Some questions may catch you off guard, but stay calm and take a moment to compose yourself. If the answer doesn't come to you at the moment, you can suggest coming back to the question. It is okay if you don't know everything, but it is important to remain professional and friendly.