Most things are not as risky as they seem.
Be suspicious of any work that is not building product or getting customers. It's easy to get sucked into an infrastructure rewrite death spiral.
In general don't start a startup you're not willing to work on for ten years.
Every company has a rocky beginning.
Move fast. Speed is one of your main advantages over large companies.
The role of the board is advice and consent. If the CEO does not lay out a clear strategy and tries to get the board to set one, it will usually end in disaster.