Learn everything there is to know about Shodan from the founder himself. The book covers all aspects from the website through to the developer API with exercises to help test your understanding.
not that extensive as I would like it to be. damn, I have to buy credits even to play with it, I wasn't able to test a lot, the only thing available for me would be the web-interface & publicly shared reports, some history data as well. John's ghost writers could be more eloquent when describing the tool they have developed themselves
3-4 stars as it does it's job, but OTOH I believe you can easily manage w/o it - content of the book ain't synthetic, it doesn't provide any broader perspective (e.g. to present some interesting scenarios Shodan can be used for) - nope, nothing of that sort. It's a pure (but accurate) description of what you can get with queries, how to shape the queries, what are the limitations, etc.
Unfortunately not as detailed as I'd hoped, but it's a great intro and reference for search terms and methods. Personally found a lot of value in the practice exercises.