Who are your customer segments?
Start by defining you customer segments. Who will you design your product for and promote it to?
Notice that I didn’t ask who you would sell it to. Of course you want to sell it to everyone who wants to buy.
In my experience entrepreneurs tend to have a very wide definition of target customers. There are a lot POSSIBLE customers and you do not want to exclude anyone. But since you probably do not have time or money to create an effective marketing to all potential customers, so it is important to decide who you want to spend your limited marketing budget on.