Resource: In-depth Interviews
Here's another great guide from Margaret R. Roller, on 'The In-depth Interview Method'. It includes 12 articles ranging from design to implementations, with a handy case study shared too. In it, you'll find useful guides to develop interesting interviews, including how to prepare your interviewees - and yourself!
A lot of this is specific to our industry, and I have some additional tips from my time as a journalist. Get in touch if you need any support with this!