Review the accounts-receivable and accounts-payable aging so the balance sheet reflects what is truly owed to and by the business. Phantom invoices and bills that were paid but never marked distort both the balance sheet and the year's income.
Chase down invoices marked open that were in fact collected, and write off genuinely uncollectible receivables only with the owner's sign-off and a documented reason. On the payables side, clear bills that were paid outside QuickBooks and confirm nothing is double-counted. The aging reports are the fastest way to spot a receivable or payable that has been stuck for the whole year.