Look at turnovers.
Another reliable way to beat the spread: Find the teams with massive turnover totals. Eli Manning's Giants have turned over the ball an unholy number of times, but everything in sports and life deviates toward the mean – especially when teams are mediocre rather than outright bad. And remember to bet on teams with erratic offenses rather than solid defenses. It is more likely that a bad offense gets away with a few fumbles and potential interceptions than that a great defense suddenly forgets how to do the job.