When I speak to a potential client I always ask, “Who is your customer?”  Mostly they do not know, or they say everyone is my customer.  Bad answer.  While you can sell everyone, you cannot design and market to everyone.  Knowing and understanding who your customer is, is one of the reasons why exceptional companies do well.
Most people forget that you actually get to choose your customers. You get to choose who you want to sell to. According to  Lincoln Murphy,  “creating an Ideal Customer Profile isn’t limiting… it’s empowering!”
An ideal customer profile is a definitive description of a customer that would find huge benefits from your product and would pay the price to acquire it.  Some companies even create an avatar. That is how detailed they are in defining their   customers.
Before you design piece one do extensive research to find out where you sweet spot is.  Study your competition and find out their demographics.  Facebook is a great tool for this.  You could go to ads manager and click on Audience insights. When there type in the companies you think you compete with and the demographics will come up.  Type in a few companies to you can get a more complete answer.  Also if the company you choose is very small they may not come up.
Another way to figure out your customers demographics is to do a focus group.  You can also do surveys.  Visit the stores you feel your product would be perfect for.  Then speak to salespeople on the floor and ask them about their customers.  Basically you need to do a ton of research in order to define your customer.  Don’t just decide who your customer is find out if you are right.  I worked with a bridal brand who decided that her customer was 30-50 years of age.  After shopping bridal stores she found that her customer was really between 29 and 32.
This is an important tip that by doing you increase your ability to be successful.