You need to know everything obtainable about your customers. This list will get you started. You will need their age, sex, marital status, income levels, education levels, geographic locations, where they shop, if they go to church, if they have kids, ages of children, political affiliation, what they like about your company, what they don't like, why they shop with you, what they value about your products/services, what they like the most/least about products/services, and whether prospects are unaware of your brand or products/services. Customers want you to know certain things about them and if you do, they will remain loyal to you as you take time to know them.
Coming back to my questions to entrepreneurs and small business owners, many of their answers sounded like this, "I don't really have one", "It's in my head coz I know the business so well" and worse, "I don't know what is marketing plan"! If you happen to be in one of these categories, rest assured you are not the only one. And to perfectly honest, that's the ultimate reason why I turned back to my writing board where I was actually in the middle of writing (rather perfecting!) a personal development programs. I dropped that program and quickly drafted and started Marketing Plan Breakthrough S6PEC because many of you need it, seriously.