Mistakes happen, and you can correct any oversights on your return fairly easily. The process is calling filing an amended return, and you'll use a special form 1040X to report changes between your original and corrected tax returns.

You can amend to report income you might have missed, or to claim deductions or tax credits you might have overlooked. One thing to be aware of is that you have three years from the original deadline to claim any refunds. So if you missed a deduction or credit for 2007, you should file your amendment before April 2011.