And something I do most of the time, but should do even more often:  Compare this year's return with last year's return.  For returning clients, there's the "2-Year Comparison" feature on ProSeries.  For new clients, you have to look at the paper copy of last year's return.  

For many practitioners, February 25 is about the busiest day of tax season.  Haste makes waste.  Take another look at last night's work, when you start the next morning.