Steve Blank, Erik Ries, and the Business Model Canvas by Alexander Osterwalder
Steve Blank’s key idea is that you ‘get out of the building’ to validate your idea, this is his website . You can watch / listen his key ideas via Udacity . it’s free, it’s good, and it’s bit sized in it’s lessons, so you can do a bit, think about it, and then do more. I did it while doing the washing up over a series of days. I found it useful.
Click on the image to go to the Steve Blank Udacity course
Then there is Erik Ries, author of The Lean StartUp. You can read it here as a pdf, buy it, and it’s in several of the local libraries too.
Finally, but a complementary tool is the Business model Canvas by Alexander Osterwalder.
You can download a free 72 page pdf, initial guide to what it is. It is clear, visually well done, and helpful to use in developing your ideas. On the website there is also a free template of the business model canvas you can download too, to help assess your business and it’s competitors.