The answer depends on several factors, and time is perhaps the most important. The longer you have until you need the money, the more risk you can take. If you don't need to tap your investments for 20 years or more, the classic asset allocation mix is 80 percent stocks and 20 percent long-term government and corporate bonds, on the principle that stocks are the more lucrative investment over time, and you're protected from market ups and downs in the short term because you don't need the money immediately. At retirement, bonds should probably constitute the bulk of your investments, though at least 20 percent should probably still be in stocks. These are broad guidelines, of course.
Different circumstances mean different allocation models.
Professional financial planners can be helpful in charting your financial future. A planner should always tell you in writing how he or she will be compensated. Fee-only planners charge a flat or hourly rate for their advice. Others get a commission for any investment products that they sell, which may be an incentive to sell certain products. Some planners also charge fees offset by commissions generated when you follow their advice.