While you should also look to self-audit, it is good business practice to bring in an external auditor. The government requires a number of businesses to hire an external auditor to look at their books and financial statements. However, you should hire an external auditor even if it is not mandatory, as it is a great way to ensure your business is in good financial shape.
This independent entity will check transactions, review your general ledger, and correct oversights and mistakes. An external auditor will also check for cases of fraud, which ensures your business is trusted by external parties.
Perhaps the #1 bookkeeping practice is to keep your paperwork safe. Make sure your business uses separate boxes for every year on record and also keeps records in fireproof boxes. If you want your business to be a success, you need to follow the above bookkeeping protocols or risk the wrath of the IRS.