I always start by comparing the income forms to the tax return and verifying that the forms have the correct SSN.

Then ask the question "Is there any additional income W-2 or 1099-R that may have been left off?" If the IRS computer has forms that were not reported on the return, this will generate a correction letter.

And also inquire about Healthcare Marketplace insurance. A return will not process if Form 8962 is missing.