The obvious areas to emphasis are at the point that cash comes into the company or where cheques are issued. Make certain that you receive a daily tally of cash received from the person opening the mail - you can then compare it to the deposit slips if necessary. Signing all the cheques yourself is a good way to control expenditures, but for bigger firms you may have to delegate this to two or more individuals. Review your bank statements every month. This will allow you to highlight any unusual amounts and give you a capsule sense of what went on in the business during that time.
Losses can occur in a few other areas.
Employees might submit dummy invoices for payment. One entrepreneur caught a person who had recreated billings with minor changes from one of the company's major suppliers. And keep and eye on submissions of personal expenses for payment for any misappropriation. The most common is mileage, entertainment and travel bills. One way to reduce your risk of misappropriation is to keep internal systems as simple as possible - anything abnormal will stand out very quickly.