Instead of investing all your money at one time, you divide your total available cash into equal parts and invest each part in CDs of varying duration.  For example, you want to invest $3,000 in a CD. Instead, you invest $1,000 in a one-year CD, $1,000 in a two-year CD, and $1,000 in a three-year CD.  Each time one of the CDs matures, you can either take the cash (penalty free—since it has matured) or re-invest it in another three-year CD to keep your ladder in place.

Here are a few sites to see what some current CD rates.
CDs are a more sophisticated and complicated way to save.  Make sure you check with your bank first.  CDs can, however, be an excellent part of your saving strategy.