Compile a target list.
You can't buy or sell a business unless you have a list of suitable Sellers or Buyers.
Contact the targets.
Making a phone call and discussing the target's interest is important. That discussion allows you to gauge the target's interest level and whether proceeding makes sense. Knowing how to make a pitch is an art, and believe it or not, being a Buyer is far more difficult than being a Seller!
Send/receive a teaser.
The teaser (sometimes called an executive summary) is the document Seller sends to Buyer to give Buyer just enough information (the product, the customers, the problem the company solves, and some high-level financials) to make Buyer want to learn more. The teaser is usually anonymous; that is, Buyer doesn't know which specific company is sending the document.
Sign a confidentiality agreement.
Both sides agree to keep the deal discussions and materials confidential.
Send/review the confidential information memorandum (CIM).
The CIM or deal book is the Seller's bible and provides all the information (including company history, product descriptions, financials, customer info, and more) Buyer needs to determine whether to make an offer.