Who is your customer?
Do you know?
Why is it important?
Knowing who your customer is will improve your income by allowing you to customize your website in the following areas:
1) Most obviously, PPC advertising. If you don't know who to target, your campaigns are unlikely to be successful. However, PPC advertising is a great way to determine who your customer is. We'll talk about that later.
2) Content marketing. You need to know who you are talking to, otherwise all that great content might be going to waste.
3) Product creation/sales. If you don't know who your customer is and what problems they are trying to solve, how can you provide them with a solution?
4) Copywriting. All of your customers have buttons that you should be pushing through emotional connections as part of your copywriting. You have to know who they are before you can figure out how they will behave.
5) Email marketing. Not all campaigns are created equally. Some of your marketing should go to subsets of your larger customer base. Do you know what those segments are and how to appeal to them? Say your customer base is made up of US football fans. You wouldn't send an email about a special on Green Bay Packers apparel to a bunch of Minnesota Vikings fans.