Don't panic. Open it. Not all IRS notices contain bad news. Check out this link at the IRS: https://www.irs.gov/individuals/understanding-your-irs-notice-or-letter
If it is an audit request, a balance due notice, or a lien or levy notice, contact your tax preparer or another professional to help you understand your options. Many IRS notices and actions have limited timelines for response. Getting a professional to assist you can make dealing with the IRS much easier. Tax law is complicated, even if the letter you receive seems straightforward. It's always a good idea to check with someone experienced in the subject.
As with all IRS notices—ignoring it doesn't make it go away. Click here to read more information