One of the best books on OSINT is by Michael Bazzell and is called:
Open Source Intelligence Techniques: Resources for Searching and Analyzing Online Information. This book is highly recommended and an excellent resource for expert or beginner.

For those of you who want to look at it from the opposite perspective, Michael Bazzell has: Hiding from the Internet: Eliminating Personal Online Information which is also excellent and shows how to remove your online footprint.

Other books on OSINT that are worth checking out:

Down the Rabbit Hole An OSINT Journey: Open Source Intelligence Gathering for Penetration Testing

Open Source Intelligence Investigation: From Strategy to Implementation (Advanced Sciences and Technologies for Security Applications)

Automating Open Source Intelligence: Algorithms for OSINT (Computer Science Reviews and Trends)

How to Find Out Anything: From Extreme Google Searches to Scouring Government Documents, a Guide to Uncovering Anything About Everyone and Everything

The Tao of Open Source Intelligence

Introduction to Social Media Investigation: A Hands-on Approach

Facebook Search: Profiles, Places & Pages: A Guide for Investigators, Journalists, Researchers & Recruiters (Volume 1)

Facebook Search: Posts, Photos & Videos: A Guide for Investigators, Journalists, Researchers & Recruiters (Volume 2)

Hacking Web Intelligence: Open Source Intelligence and Web Reconnaissance Concepts and Techniques

Open Source Intelligence Analysis: A Methodological Approach

Investigation books:

How to Become a World-Class Investigator: An Insider’s Guide to a Secretive Industry

  • The era of the lone wolf private eye is over. Julie Clegg’s essential guide to twenty-first century investigations illuminates a bold new path to success in this exciting and rewarding field while effectively debunking the culture of secrecy that has always pervaded the industry.
  • Few careers offer the challenges of investigative work and fewer still afford the opportunity to make a real difference. But in the information age, working solo in the dark not only hinders investigation, but threatens the entire industry.