If you don't know how to build a community of potential buyers before you have your final product, it's very likely that you're also not going to know how to do it once you've got your final product ready. So better to start thinking about it before you start panicking because no one's buying it. A cool bonus: Once you have a community of potential buyers it's a lot easier to figure out what they really want instead of offering them something that you think they might want (but probably don't want)...