Most interview tips are applicable no matter where you're interviewing, but several people have asked me if there's anything they should keep in mind when interviewing with a non-profit organization. I've interviewed at a number of different non-profits, so I have a handful of tips of things to be mindful of when you've landed an interview at one of these organizations.
Employees at a non-profit are used to having to sell their organization (e.g., to donors), so an interviewer may spend too much time talking and not enough time letting you talk. One way to get an interview back on track if this happens is to find a natural pause and say something like, "That sounds great. How could I help support that work as [position title]?" Or you could offer up experience you have that is similar and then mention how you'd love to do that again in this role. That will help remind them that they need to be more focused on finding out about you than telling you about the organization.
Non-profits tend to be smaller and not necessarily have a dedicated HR person, so you'll often be interviewed by multiple people. Make sure you're making eye contact with everyone while you talk, not just the person who asks you the question. I suggest having a variety of different questions prepared ahead of time, and then as you learn what each person's specialty is within the organization, you can ask questions specific to their areas of expertise. This also helps with personalizing your thank-you notes after the interview.
Just having an interest in "helping people" isn't enough to stand out as a candidate. Be as specific as possible in talking about why their particular mission is important to you. Most non-profits will explain on their website why they do the work that they do, and what their organization does that's unique from any other organization in the local area; you should be well-versed in this and be able to articulate it yourself, as well as tying it to your own past experience or interests.
Unlike for-profit businesses, which tend to be cubicle farms, non-profits often have a lot of programs and activities going on right in the same place where their offices are, so for in-person interviews they may also take you on a tour of the space. This is an opportunity for them to get a sense of how you interact with the people they serve. Don't clam up if this happens; use it as just another opportunity to show how well you'd fit in at the organization.
Finally, remember that this is about finding a match, so you should feel comfortable with the organization and be able to envision yourself there. Don't try to be someone you're not; look for an opportunity to find the right fit for your skills and passions.