Monitor your books yourself.
This is an obvious practice, but a very important one. Do your best to set aside time each day or month to review and monitor your books, even if you're working with a bookkeeper. It will allow you to become more familiar with the finances of your business, but also provide you with a window into potential financial crime.
Do not neglect bank reconciliations and spending some time each month on reviewing outstanding invoices. Failing to do this, especially if a bookkeeper is involved, opens up the business to wasteful spending or even embezzlement.
Shameless plug: having a third set of eyes, like a CFO, can also be valuable to monitor and understand the business finances.