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.
Competitive Edge: It's important to define your competitors too. One should know, what strategies are being used by the competitors to reach to the potential customers. If you know what your competitors are doing, you will be able to modify the plan and maybe your marketing analyst will come with something more innovative that can capture the mass attention.