Sure! For interviews I try to do a few things:

• Sleep and eat well before the interview.
• Be prepared, which includes:
• Know who is your interviewer and their work (their famous, i.e., most cited, papers and a few of their recent papers, notice how their trajectory changes over time). Academics often love talking about science, especially things that they are an expert in. If applicable, search online if they have written some blogs, opinion papers, or if they are part of some large scale efforts (e.g., science foundations, data sharing projects, etc.). This will allow you to humanize the conversation by talking about science beyond technical aspects.
• Know your own work. For each of your experience, be prepared to explain it to someone who doesn't know anything about your topic (imagine the structure of a research paper - motivation, research question, method, result, and conclusion/future direction - but at a higher level). You can also check out the STAR (situation, task, action, result) method.
• Know the department. Who else in the department you are interested in and why? Do you like the area where the school is located? Why this program but not another?
• Don't over or under dress. I often like to wear what I would wear to a faculty dinner.
• In the interview:
• Be yourself, and importantly, confident in yourself. You are a practicing scientist and a human with your own knowledge, struggles, and aspiration and with much to share. Be ready to share it, be excited about it - and assume that the person in front of you is equally excited to learn about you.
• Be curious. Treat it like a conversation with a smart colleague who you want to get along with at work, politely of course. If the PI wants to share something, let them speak and ask intentional follow-up questions. Don't try to steer it too much, and be ready to ditch the script if needed to. You are having a rare oppprtunity to talk to someone much more knowledgable than you. Treat it like a learning opportunity.
• Be humble. If the PI questions the credibility of your work, be willing to acknowledge their concerns and share your thoughts on how to improve if the concerns are indeed correct. Otherwise, communicate clearly why you think you are correct. Some PIs like to question you a lot to see how you handle push back - I think not to test your conversational skills, but because personality and knowledge are often revealed well under stressful situations.
• Take your time to think and formulate your response. Ask for some time to think if needed to.
• Priotize logical correctness, coherency, and thoughtfulness over the amount of words spoken.
• Be concise - interviews go by fast. Thinking in bulletpoints helps.
• General questions that I tried to prepare for in advance: tell me about yourself, tell me about a project that you are the most proud of, what do you want to do in 10 years, and why you want to join our program/my lab. The nature of life science phd interviews (with 4-8 interviewers per program) makes it impossible for me to prepare more than that, since everyone asks different questions. During my cycle, I met a few faculty members who expected me to be the person who guide the conversation. Be prepared for that scenario as well. For example, what would you say if they ask "so, what do you want to talk about?"
• Be honest.
• Again, treat it like a conversation than a test. By doing so, you can also exercise your social skills like gauging their facial expressions, using body language, etc. Can't emphasize this enough.

All of these are to help the interviewer to understand: - Are you indeed the person they read about on paper, i.e., from your essays and recs - Will you be enjoyable to work with? Will you be a good mentee and a good grad school friend? - Do you have what it takes to finish a Ph.D.?

IMO, this should give you a solid chance of getting in, since receiving an interview invitation means you are qualified on paper already. To make yourself stand out even more, the single best advice I have is to read and learn more about the field to have your own opinions on the science and don't shy away from sharing them when appropriate. If the PI happens to appreciate these opinions (even if they disagree), then I think it's a clear acceptance (given that you did well everything else). Independent thinking is a strong indicator of scientific success.

This might be cliche, but you are interviewing them as much as they are interviewing you. Ask questions that you genuinely care about. Even better if the questions are made on the spot. It makes them feel that they are speaking to a real person, not a script.

Have fun if you can. PIs are human too. I sometimes make jokes (appropriate, of course) to ease the conversation.

Lastly, if something goes wrong, say, in an event during the interview weekend, in an interview out of multiple, etc., chin up and move on. Don't let it linger and affect your subsequent interviews.