Before approaching a prospective private-label customer, prepare a prototype package similar to the packaging that company uses. Take a high-quality picture of the package and of your product in use, and prepare a one-page sales flier highlighting your product's key benefits. Next, call the president or marketing director at the company and ask if they would like to take a look at a product they could purchase under a private-label agreement.
Contact only one company at a time. Companies want exclusive arrangements and don't like taking on products that have been "shopped around" to a lot of manufacturers. Tell the manufacturer you've chosen to approach only them because you feel your product is a perfect fit for their business. If they show interest in purchasing your product, send a cover letter and your sales flier. A week or so later, call back to see if they would like a sample.