While most taxpayers are never audited by the Internal Revenue Service (IRS), there's always a possibility of making an error when filing your return. These mistakes can lead to audits, and the Treasury Department can capture a 400% return on investments when they conduct these audits. One of the first mistakes is leaving all of your tax returns to the last minute, as you'll make mistakes or leave things out and get audited. Obviously, if you don't file your tax returns, the IRS will be the first to knock on your door and even quicker to administer penalties. If your earnings have taken a significant hit, you will obviously pay less taxes, which the IRS may be suspicious of as they have your tax history. People who file their returns on paper rather than digitally are 20 times more likely to make a mistake due to human error. Lastly, make sure you've accounted for all of your accounts and be diligent in ensuring that your old 401k account is included in your returns.