Once you’ve created (and, preferably, automated) a habit of saving each month and invested your money into a target-date retirement account, it’s best to forget about it. “Setting and forgetting is the only thing that works,” Chatzky says, adding that when the markets are down, it can be tempting to make rash decisions. However, it's in these times that you’re actually more likely to make gains, since you'll buy more shares at a lower price. “When markets are down, hold on to the number of shares, not the price of what you're buying," Chatzky adds.