Great question! Here are the basics:

The Lean Startup by Eric Reis
http://www.amazon.com/The-Lean-Startup-Entrepreneurs-Continuous/dp/0307887898

Running Lean by Ash Maurya
http://www.amazon.com/Running-Lean-Iterate-Works-Series/dp/1449305172/ref=pd_sim_b_4?ie=UTF8&refRID=03VER05GWM6QV80D49ZH
*excellent, concrete, super actionable

The Startup Owner's Manual by Steve Blank
http://www.amazon.com/The-Startup-Owners-Manual-Step-By-Step/dp/0984999302/ref=pd_sim_b_3?ie=UTF8&refRID=0JNJVNK8B46D6M98W1A5
*the bible!

Lean Customer Development by Cindy Alvarez
http://www.amazon.com/Lean-Customer-Development-Building-Customers/dp/1449356354/ref=sr_1_1?s=books&ie=UTF8&qid=1429290160&sr=1-1&keywords=customer+discovery+validation
*focused on methods you'll need to use to validate feature and value prop ideas

When in doubt, **stop debating**. You are not your customer. Get out of the building. Don't build unless you're testing what you build, and ready to throw away what you build when you get answers.

Good luck! Books are helpful as background, but for specific advice on where you and your company specifically should invest time, set up a call with me.
https://clarity.fm/caneel