Before product/market fit, your only job that matters is to build a great product.
If you're not in college and you don't know a cofounder, the next best thing I think is to go work at an interesting company.
A third advantage of mission oriented companies, is that people outside the company are more willing to help you.
The cost of getting an early hire wrong is really high.
You really want to know your cofounders for a while, ideally years.
M&A negotiations feel really fun. This is one of the biggest killers of companies, is they entertain acquisition conversations.