My 2 cents from my personal experience, finding a mentor is a 2 way street. You have to like them and they have to like you. Why is this important? You're going to ask them for a letter of recommendation most likely. They're going to be someone you're going to spend a lot of time with. If it feels like you have to force yourself to kiss up to them, instead of genuinely being nice to them because you like them, that's a red flag. Your personality types have to match too. My mentors in research have typically been people who give me a lot of independence and autonomy whether because they were too busy and/or had faith in me, I don't know.
I do research in a metropolitan area so there are plenty of research opportunities and it becomes more of a two way street. I work for free but my mentor not only has invested thousands of dollars worth of supplies and man-hours to train me but also has been kind enough to help me apply for all sorts of grants. She is someone who supports me and you need to find someone just like that. You also have to find the research interesting. You have to want to come in whenever you can because in my opinion, if you're not putting in at least 10 hours a week into research, you're not going to get much out of it.
The work environment also has to be to your liking. You don't want to go work in a place where you feel like you don't belong. From my informal interview with my lab, I could tell the kind of people that worked there. They were genuinely kind and hard-working. Many of my friends tell me about how they're stuck washing plates and beakers all day or that PhD students and other undergrad students try to steal their work. On the other hand, the people I work with will let me use reagents and supplies that takes them hours to make (I, of course, always return the favor whenever possible). The informal interview is to see if you're a good fit both for you and for them. I would suggest reading up on some of their work. They will likely introduce you to the lab. Even if you find out mid-way through the interview that you're not interested, always act interested in the work and send them an email later thanking them and politely stating you're not interested if you aren't or that you are and politely ask what the next steps are assuming you don't screw it up by saying something like "Wow, this lab blows.". Remember, researchers love it when they get the opportunity to share their research with someone who finds it interesting. However, ultimately, remember that you are an investment of their time and resources if you decide to join and that it is a privilege, not a right, to be able to do research even for free.
Just don't freak out. Some of the research is at a doctorate level so it might seem a little gibberish to you but they can usually boil it down for you and its actually an opportunity for you to ask questions.
