It's become popular in recent years to say that the idea doesn't matter.
No matter what you choose, build stuff and be around smart people.
Two other things that we hear again and again from our founders, they wish they had done earlier, and that is... simply writing down how you do things and why you do things.
Most founders have not managed people before, and they certainly haven't managed managers.
Move fast. Speed is one of your main advantages over large companies.
AirBnB happened because Brian Chesky couldn't pay his rent, but did have some space.