How to Pre-Sell a Product

In most web ides that have started, i was able to pre sell a product before i even had. traffic come to my webside. For example, step one, the book. I sold ten copies of the book before i wrote a single word and before i even sent it out to my email list or posted about it on my wepe side. But really, i don't do anything complex. I try to keep it as simple as possible. D just o get the presals in the door, and then we can start talking about the product of what its going to look like. Ye. Ya make son, and what dare you used for apesas what's offer?