It is grad school interview season,which means it is the last piece of a VERY stressful application process for many. While it is important to impress interviewers, it is crucial to find a place where you'll be happy. Here are some things that helped me decide when I interviewed:

There are mainly three categories you'd to ask questions about: the program, the lab and the PI. I tried to focus on my expectations and priorities but feel free to customize. Try to ask the same question to multiple people to get some inter-rater reliability if time allows.

For the program, I was curious about the training on grant writing and quantitative methods as well as the opportunities to get help with presenting/publishing research; the research centers and how they make use of them (i.e., what sort of help they offer for fMRI analyses).

Ask about the particular trainings you are interested in. Also what is the community like, how the faculty make sure to be involved in taking steps to resolve issues should they arise, are good mental health resources available, is it a competitive or a cooperative department...?

For time managing purposes, department/program-related questions are good to ask profs you are not particularly interested in working with or grad students from other labs.

For the lab environment, grad students in the lab you are applying to would be a good resource but I would also make sure to ask other students in the department to cover all bases because there is always a conflict of interest and different power differentials at play.

If there is a problem in the lab that you should know about, word gets out and people in the department would be able to talk to you about that. There are a lot of stories about emotional abuse and mobbing in academia, which you would not want to be a part of.

Ask grad students in the lab you are applying about the mentoring style of the PI, social life in the lab, peer support (more often than not, lab mates contribute to each others training tremendously), co-authorship on papers and distribution of responsibility for lab projects.

It is a very good indicator of the lab environment if a student(s) left the program or changed labs in the past. If there was a case like that, try to ask why. It might just be for personal reasons, which happens. You'd, however, want to see if there is a pattern of abuse.

Work life balance might not seem like a big deal when you are starting with a lot of excitement but burnout is real. Make sure to ask both students and the PI questions about the workload, how much time you'd be expected to dedicate, how much time they take off each year, etc.

Ask student what their day-to-day looks like. It gives you an idea about how your life is likely to be in the next ~6 years if you end up working in that lab. Do they have time for a social/personal life, how often do they visit family or get drinks with friend,...?

Accessibility of PI when needed is very important as more senior profs tend to have so many responsibilities that they might genuinely forget about their responsibilities to you. How soon you get feedback on paper/poster/symposium submissions can be critical.

The type of feedback you receive is also important (you might prefer point-to-point edits or general comments depending on where you think you are, and it is a matter of personal style that tends to be stable so chose wisely). Be honest with yourself about your needs.

The area! You are probably moving to a new place you will be calling home. Though you'll spend most of your time in the office/on campus, you'd still want to be somewhere that can accommodate at least some of your needs/wants. If it was in-person,you'd talk about it during dinner

For the PI, following from the previous points, I would directly ask how they handle burnout in grad students and what they advise when the workload is too much for a person or if they have personal problems. You'd not want to hear a robotic answer to this.

It is important to have a PI that is supportive of your physical and mental health because you are likely to have AT LEAST one health problem in ~6 years and you really would not want the extra burden of dealing with a demanding boss who does not care.

Their mentorship style,how your grad school life'd look (the big picture questions like do they start you off with a project or are you expected to come up with something on your own in the first year),is there a specific project they think would be good for you to start with+

(research interests change and you might be there for the beginning of a new chapter), what kind of trainings they offer, what is the structure of lab meetings (again, not every lab has so many meetings. in fact, some meet only once a month/semester)+

how often they they would want to meet with you 1-1 (I have seen people who meet their advisors once a year!) are all good questions the answer to which should match your expectations and priorities. It is also OK to ask specific things you'd prefer to have in your training.

It is crucial to know if they have a plan to prepare you for the nonacademic job market (even if this is not something you are interested in now, you can ask what is the typical career path for their grad students after PhD and whether anyone went on to doing something different)

I would just openly and very clearly ask what they expect from a grad student. You can ask them to describe the “perfect” grad student/mentee. This helps you decide whether it is a good fit.

For clinical psych: Ask whether they have child/adult pracs, what kind of internships their students go to, what year do students typically go to internship and (if >5) is it students' choice to extend the program. Licensure rates, internal prac, external prac sites in the area+

interdisciplinary collaborations within the department, ease of getting your hours in the clinic (if they have one) and the model of supervision are also things you'd want to learn before choosing where you want to go.

Be open about your expectations, priorities, and limits. Applicants often feel desperate (as I did) and try to say "just the right thing" to get an offer. This is a LONG road. You want to make sure you are somewhere you feel supported in every way, academically and emotionally.