On Monday, Sept. 29, the Dow Jones Industrial Average took its worst hit since the September 11 terrorist attacks, and investors have been riding the stock price rollercoaster since.

As the economy and market struggles, it's a good time to make sure you're taking the right steps to protect your portfolio. The CFA Institute, a nonprofit that serves investment professionals, says these are the most common mistakes made by investors. Make sure you're not making any of these missteps yourself.