1. Make a Brand

Create a brand that embodies you and your design aesthetic. Consider how you will use the brand across the board, including packaging, marketing materials, a website, company documents, and so on. Your brand may always be tweaked later, but focus on identifying the essence of your brand right away. 

2. Network 

Don't be scared to put yourself out there and meet new people. Also, don't limit your search to invitation designers. Others who operate their businesses, regardless of their competence, are brimming with advice and lessons to be learned.

Don't think of networking as a means to make money or get more business; instead, think of it as a method to connect with and learn from people who have gone through similar situations, which will help your business flourish.

However, keep in mind that they are not there to provide you with all of the answers. You must put forth the effort to uncover the answers on your own, but they may correctly point you.  

3. Understand Your Customer

Create an introductory questionnaire that includes questions to assist you to understand the personality and style of your potential customer. What do they hope the correspondence will convey? What mood or tone do they intend to portray with their invitations?

The better you understand your customer, the more you will be able to incorporate their individuality into the design (assuming you do custom work). Isn't that what it all boils down to?