It's never too early to start. Your first step: Take stock of all your assets. These include your investments, retirement accounts, insurance policies, real estate, business interests and valuable items - in financial or emotional terms - such as jewelry, cars, baseball card collections or your great-grandmother's good china.
Next, decide what you want to achieve with those assets and who you want to inherit them. This is also the time to think about people you would trust to handle your business affairs and medical care in the event that you become incapacitated.
After you decide what kinds of bequests you wish to make, discuss your plans with your heirs. The sooner and clearer you outline your intentions to your family and friends, the less chance there will be for disagreements after you're gone.