The most common diversification suggestion is to divide a portfolio among stocks (which can offer big pay-offs but can also be high risk) and bonds (Treasury bills that offer little to no risk, but pay out less than stocks). Depending on who you talk to, you'll hear different percentages for splitting your portfolio between stocks and bonds. One good rule of thumb is to keep your bond percentage close to your age adjusting as life goes on; so if you're 30, about 30 percent of your portfolio should be in bonds. By the time you retire, 60 to 70 percent of your portfolio should be in bonds.