Can't get the thrilling bank robbery scene from The Dark Knight out of your head? Need a quick windfall to make ends meet or just have to head to a tropical island with a suitcase full of hundreds?

If you dream of telling a bank teller to stick-em-up, here's what you should know: The vast majority of bank robberies are relatively unsuccessful affairs, having netted criminals just $7,500 in 2010 on average, according to the FBI.

But if you're going to start taking after Bonnie and Clyde, there are some things you can do to up your take, according to an analysis of British and American bank robberies by researchers at England's Universities of Sussex and Surrey, published in Significance, the journal of the United Kingdom's Royal Statistical Society.

Pick a Target—In 2006, the average bank robbery netted about $4,330, compared to an average of $1,589 for all commercial robberies. Avoid convenience stores—the average take there is just $769.

Better yet, go to England, where the average bank robbery nets the U.S. equivalent of $31,500. Don't worry about which bank you target—the study found that branch size and whether the bank was in an urban or rural setting had no impact on average amount stolen. However, banks with fast-rising security screens that block off tellers from would-be-bank-robbers seem to help,according to the study. They severely reduce the likelihood of a large windfall.

But with most robbers taking a mere pittance and bank robberies being a relatively rare crime (there are more than 6,000 commercial banks in the United States and thousands more credit unions), it's barely worth it for banks to invest in the screens, which cost a couple thousand per teller window to install.

The monetary losses of bank robberies are "generally not what most concerns the banks," according to the Significance study. "The psychological costs borne by staff, and by clients who happen to be in a bank at the time, are not small."

Brandish a gun—In England, bank robbers who threatened employees and customers with a gun stole, on average, about $16,000 more than robbers who were unarmed. Of course, showing off a gun raises the risks as well—armed robbery almost always comes with a minimum jail sentence and makes things more dangerous.

According to the FBI, in 2010, 16 people were killed during bank robberies—13 of them were the perpetrator. Of the 5,500 American bank robberies in 2010 only 1,445—about a quarter—involved a gun. Most commonly, perpetrators used a demand note or the threat of a weapon, without actually showing one.

Use a team—According to the study, for each additional person involved in a bank robbery, the criminals can expect to add about $14,000 to their take. That might result in a lower per-person haul, but the researchers say using a larger gang has other advantages.

"It is advantageous to divide tasks—monitoring the bank lobby, accompanying staff to vaults to ensure maximum takings, driving the getaway car and so on," they write. "In short, it may be more professional, and the larger returns may reflect that."

Lawyer up—In the United Kingdom, about 20 percent of would-be bank robbers get caught and go to jail. According to the FBI, the cash stolen in bank robberies was recovered in about 22 percent of successful robberies in 2010. If you make a habit of it, by the fourth bank robbery, you're more likely to be in jail than walking the streets.

Don't do it—Overall, it's probably not worth it to attempt a bank robbery, the researchers conclude. "The return on an average bank robber is, frankly, rubbish," they write. "It's so low that it is not worth the banks' while to spend as little as [$7,000] per cashier position at every branch on rising screens to deter them."

More people seem to be taking that advice: In 2004, there were more than 7,500 bank robberies in America, 26 percent more than there were in 2010. According to the researchers, "robbing banks is no longer what you could call the crime of choice." But they do have some other advice: "Security vans offer more attractive pickings."

Jason Koebler is a science and technology reporter for U.S. News & World Report. You can follow him on Twitter or reach him at jkoebler@usnews.com