1. Not claiming the Making Work Pay credit
Last year, your paychecks probably were slightly larger thanks to the Making Work Pay credit that was enacted as part of the 2009 stimulus bill. That change was thanks to adjusted payroll withholding tables, but to officially get that credit, you must claim it on your tax return this year. Filers who use Form 1040 or 1040A will need to send in Schedule M. Those who use Form 1040EZ need to complete the work sheet on the back of that form.
The credit is worth up to $400 for individuals and $800 for married couples filing jointly. The IRS says many taxpayers are omitting Schedule M. While in some cases the IRS is processing those returns anyway based on information reported by employers on workers' W-2 forms, that added work is slowing down the process, meaning refunds are not going out as quickly.