If you are using the interview for fiction, it is easier to incorporate the facts within the story, and you don’t need to document the minutes of your interview. For example, if you are writing a science fiction story about an intergalactic band of rogue aliens smuggling humans, you may want to interview an authority on law enforcement to understand how smugglers operate. Interviews for writing fiction does not need footnotes, but some authors include it along with their references at the end of their novel or mention invaluable contributions of people in their acknowledgments. 

Nonfiction is a different ballgame and requires more diligence in citing sources. Follow the standard rules of usage in the citation style of your choice (Chicago, MLA, AP, APA, Turabian, etc.). Document the time and date of your interview and the statements of your source must be included in the bibliography. You may also want to include them in your acknowledgments.

While we’re on the subject of quotes, it is a no-no to alter quotes even if you are compelled to for grammatical reasons. For this purpose, inform your subject or source that their statements will have a little “clean-up” for grammatical accuracy. Most of the time, they will agree. Nobody wants to be embarrassed by the wrong grammar.

Facts from your interview lend credibility to your tale so that it becomes believable and three-dimensional. Many writers of detective and crime fiction are known to tag along with cops in their nightly rounds. They visit courthouses and watch criminal hearings. They talk to lawyers and forensic experts. This is why a good detective or crime fiction keeps us on the edge of our seats. The information these writers obtain from talking to people with the necessary know-how tells us that the story may be fictional or coincidental, but it could happen.

I once wrote a science fiction story about a race of militaristic aliens that were encroaching on our planet silently and they begin with remote, provincial territories to keep it low-key. I researched weapons and made a field trip to a remote barrio and blended with the locals--even staying with one family for a few days. This barrio became the setting of my story. I had also gathered that it was a hotspot for insurgents, that government forces often deployed patrol units and checkpoints to monitor unfamiliar faces. My host family forbade me to go mountain trekking because I might be mistaken for an insurgent. My experience, along with the information I had gathered from talking with locals, helped me to flesh out a setting with pulsating local color. 

I believe that every person is an expert on something--even mendicants and the homeless. These people can tell you a thing or two about harsh living conditions. Interviewing is an essential part of writing. Set a time and schedule to talk to people, so that your research does not interfere with your writing time. Flimsy writing is often the result of insubstantial information because the writer is too lazy to go out and talk to people. Another benefit to interviewing is that you grow your connections. If you ever find yourself writing about a similar topic in the future but with a different bend, it will be easier to contact your expert.