I've owned a business for many years and would like to sell it. How do I start the process?

First of all, Assemble a 'team' of professional advisors that would represent your best interest in the transaction. Your team should include an experienced business broker, an attorney and a CPA. There are many considerations in the sale of a business and each professional would lend their expertise. You may want to consider a 1031 exchange which would allow you to defer the capital gains tax upon the sale.
A 1031 Exchange has critical date requirements that need to be met and your accountant can advise you on this process. You may also consider seller financing to provide you with a long term annuity. Your attorney can assist you in structuring a contract for deed or purchase money mortgage. An experienced business broker can provide the marketing and expertise required to attract qualified buyers and negotiate the sale on your behalf. This 'team' approach helps to insure all of the considerations are handled professionally and that your sale will be consummated smoothly.
Secondly, the buyer of a business wants accurate information. The more information you can provide a buyer, the better the chances of selling your business. This includes tax returns for the most current 3 year period, a list of personal property that may be included in the sale, professional photos of the business; including aerial photos if real estate is included, description of the building, a copy of the lease if the business leases its facility, etc. Once this information is sent to a potential buyer, the buyer may request additional information specific to the business. A seller that is unwilling or unable to provide accurate and detailed information will have a difficult time selling his/her business.
Thirdly, an experienced business broker will be certain that any inquiries will be held strictly confidential. It is imperative that confidentiality be maintained and your business broker will require a signed Letter of Confidentiality of anyone inquiring about your business.