1. Make sure your products pass the necessary tests. I come from apparel so I see some similarities in requirements for safety. When you feel ready to start your outreach with large retailers, make sure you have all the legally required testing done for your products. The retailers will ask for them or will ask you to confirm that the testing is being done and is in line with the state and federal requirements.
2. You also need to have proof of concept in place. By that I mean you need to prove that your product sells and is not just a fad. It helps for them to know that you have been in the boutique space for a while and your products have sell through not just sell in.
3. Be Where the buyers are. Make sure you are going to tradeshows where the buyers of the national retailers are going. You won't get orders at your first show. You probably have to go a few times and rub shoulders with both exhibitors and vendors until your face and brand are recognizable. You also improve your chances of strengthening point # 2 by following point #3.