A written sheet about what your product is and who is your audience.
Note any successes that any other store has that is currently carrying the product.
Step1
1. I'm not an expert at this, but my mom owned a bookstore for a few years and was approached many times about product displays.
Step2
2. Decide which stores would be best for your product. who would use your product? where do those kinds of people shop?
Step3
3. Make a impressive information sheet that you can hand out with a picture of your product. What it does or can do and who could benefit from it, and if anyone other store is currently having success with it.
Step4
4. Always ask to speak to the owner. It is rare that your information sheet or phone number will be passed on from an employee to the owner. Ask when a better time would be for you to come back to meet him or her.
Step5
5. Most stores are apt to "try" your product on their shelves if it is no risk out of their pocket. Ask if you can display the product and if it sells then a portion of it will go to you. If the product sells well, the owner will want to buy in bulk!
Step6
6. I hope this helps. Again, i'm not an expert...but i do know what i saw would work.