Start with your adjusted gross income, the figure on the last line of the front of your 1040 or 1040A tax form (line 37 for Form 1040, line 21 for Form 1040A, or line 4 for Form 1040EZ).
Then find yourself a calculator, and add back:
Any deductions you took for IRA contributions.
Any deductions you took for student loan interest or tuition.