I'm in same position as you, and would love to know if you're open to partnering up but to answer the question I've found the following very useful so far.
there are more but these are what i've read so far and liked.
Main points I've learned...
Build nothing, or as little as possible. Think of vision, say craigslist, don't build it. Build stairs to it, dig a path to it. Start weekly email letter with website as complementary to save emails. Grow from there.
If it's b2b, do selling first, nail down how to approach, who to approach, what to sell, for how much, get 5 people signed up before writing a line of code. Free or not, get people on board.
prioritize speed and delivery over all coding standards, security standards, and over everything else.