One of the best things you can do as a CEO and board member of your own company is to serve on another company's board of directors. There's nothing like a real-life counterpoint to make you take a step back and think about how to build and run an effective board. Find something—another startup, a nonprofit, your high school or college alumni association—to join as a board member. Watch and learn how other leaders lead and how other boards present materials, run meetings and discuss thorny issues. You might have the bandwidth to do one or two of these but probably not more.
First prize is to serve on the board of directors of a company that looks generally like yours, though probably smaller or earlier stage. Second prize is to serve on another noncorporate organization's board of directors or board of trustees. Third prize, though still quite relevant, is to serve on another organization's advisory board.
You can add a lot to another board and organization based on your experience, which is unique and powerful. The best advice I can give you is that you should do two things as you sit on another board.
Be the board member that you want on your own board. Be honest and direct. Be constructive but don't hold back. Do your homework, come prepared for meetings and pay attention.
Don't hesitate to vet the organization and board before you join it and don't hesitate to quit if you can't have an impact ...