After the sale of your business is completed, the first thing you should probably do is take a well-deserved vacation!
The process of selling your business can be very hectic. You've probably put a lot of work and many late nights into gathering and presenting information about your business, schmoozing with potential buyers, and negotiating the terms of the deal while at the same time trying to keep your business running with at least a semblance of normalcy. After you close the deal, the exhaustion will probably hit you, as well as the emotional impact of having to let go of your company. It may be a good idea to leave town for a while, so you can avoid seeing your "baby" in the hands of a new owner, at least until you have some time to adjust to the change.
You may continue to be tied to your former business for a few years, if you've agreed to stay on as a consultant or employee, or if the new owner still owes you money. But chances are you'll be much less involved in the day-to-day routine, and more concerned with strategy and long-term direction. And even this involvement is likely to be fairly short-lived, as the new owner begins to feel more comfortable and anxious to make his or her mark on the business.
Most of your attention will turn to the best way to put the proceeds of the sale to work. You'll probably want to schedule a meeting with your attorney and financial planner to determine whether there are any creative ways to structure your holdings. For example, if your former business was incorporated and the assets were sold, you may be able to use the corporate "shell" to shelter revenues with a new defined-benefit retirement plan (the old corporation may continue to receive income in the form of old accounts receivable, payments on a note from the new owner of a business, or rent from business real estate that was not transferred in the sale). Alternately, you might decide to liquidate the corporation. A trust or family limited partnership may be the best way to shelter some income or transfer it to family members in a way that will minimize income taxes now, and estate taxes later.
If you haven't spent much time learning about investments, now is a good time to do it. If you have a significant amount of money to invest you'll probably want to seek the help of a professional advisor, at least in the beginning. But that doesn't mean you should avoid learning as much as you possibly can about the world of finance.
Finally, many former small business owners who've successfully sold their companies find that they miss the challenges and risks that go along with being an entrepreneur. Many have found that they can scratch that itch, and at the same time achieve a good return on capital, by investing in other small businesses in their town or region. Becoming a business angel who can come to the aid of younger entrepreneurs with both money and expertise can be the perfect solution to the question of "what do I do now?"