For bonds, we'd recommend a 50-50 split between funds with average maturities of one year and five years. This should give you the optimum combination of return and stability. We recommend you choose index funds whenever possible instead of funds with actively managed portfolios. You probably won't have those exact choices in your plan. But most plans have a money-market fund or equivalent.
Most plans have at least one bond fund.
Anything called a short-term bond fund will put you in the right ballpark. You'll usually have at least a few choices of stock funds. Descriptions of other U.S. stock funds will sometimes tell you if they specialize in small companies or value companies. If you have only one, use it for 40 to 50 percent of the stock part of your portfolio. If you have more than one international stock fund available to you, look for ones whose investments are broadly diversified over many countries and regions.