There are only a few sites I refer founders to these days. The first one is usually Steve Blank's.
The primary problem I see with founders--dozens of them--is they don't know their model. Steve focuses you on some key questions that seem so obvious, yet so many people miss them because of an obsession with vision, or product, or raising capital.
You have to start with the customer. Who do you serve? Who pays you? What do you they pay for? How often will they pay you? And how, exactly, do you know this?
Steve has a new book. Go check it out.