What are you selling?
Goods or Services?
It doesn't matter actually... you need to know the same information - who is your target audience? By understanding who they are, where they are (or more importantly where they shop), what and how they buy and why - you are in a much better place to help them. You can have many target audiences (in fact you really should) but you need to understand them.
You need to be where your clients are looking so they can find you. Where is the best place for you to have a presence & what do you need to do to attract your audience and help them buy?