You can read our in-depth informational interview article by our founder on Hackernoon.
Key question #1: With so much information available on Glassdoor, Vault, Linkedin, and public media, why do it? Answer: Building a relationship.
Key question #2: How to do it so that you are not redirected to the resources above? Answer: Make it specific to department, role which generic descriptions could not answer.
Key question #3: We all have limited time, which informational interviews are worthwhile? Answer: The ones you believe can be converted to a job referral.
Good luck out there!