First, set aside a cash cushion. You should have two to five years' worth of living expenses in highly liquid investments, such as savings accounts, money markets, and CDs. If you have other sources of income, such as Social Security, you can reduce the amount accordingly.
If you are confident in your portfolio's ability to last throughout your retirement, you can keep closer to five years' worth in these highly liquid accounts, because you may have less reason to take on additional risk.
Next, determine an appropriate asset allocation. Looking at target-date funds for your retirement date can help give you a sense of an appropriate breakdown, but there is substantial variation between target-date offerings. Some target-date providers emphasize reducing volatility and have more conservative allocations. Other target-date funds focus on minimizing "longevity risk," or the possibility of outliving your money. These have more aggressive allocations.
If you're not sure which side of the longevity-versus-volatility debate to come down on, you may find it helpful to look at the median weightings in each asset class in an effort to arrive at a target date fund "consensus" view of appropriate asset allocations for those in or nearing retirement. See this article for more details.
Once you've set your allocation, it's time to deal with your actual investments. Revising your allocation may simply require adjusting your existing holdings, or you may want to add a few new ones. You'll want to add inflation protection to your portfolio--as you shift more of your portfolio into fixed-income, it becomes more difficult to keep pace with inflation. This article details the process of getting a portfolio retirement-ready.