Choosing how to invest retirement savings often ends up being a dartboard exercise for younger people, because it all seems so theoretical.As the date of retirement or semi-retirement gets nearer, however, you begin to realize that your financial choices have serious consequences. How you divvy up assets among stocks, bonds and other investments can be a key determinant of your future quality of life.And once in retirement, it becomes crucial that your mix of assets matches your individual tolerance for risk — because you probably won't have a second shot at it.Here's a primer on how your money should be invested in retirement:•Think about cash first. Before the 2008 financial crisis, financial advisors usually suggested that retirees keep six to 12 months of living expenses in cash accounts such as bank money market accounts. Now, the typical recommendation is much higher — reflecting the trauma that investors suffered. ... Sandi Bragar, a principal at wealth management firm Aspiriant in San Francisco, said her firm expects the bond portion of clients' portfolios to generate total returns averaging about 3% a year over the next 10 years, while they believe that U.S. stocks could return 6% to 7% a year.But stocks carry much more risk than bonds, particularly over short periods of time. Of course, bonds have their own risks. If inflation ever rises again, and market yields on bonds jump, older fixed-rate bonds will fall in value (though they'll still be paying interest).You can help mitigate those risks by spreading your bond investment over short-, intermediate- and long-term securities. And if higher interest rates are coming, that won't happen overnight. You will have some time to adjust your portfolio, if necessary.