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.
Marketing Plan: In this you perform, precise activities which helps in achieving the goals and objectives you are targeting at. Here, you plan how you will promote the product/service? What are the specific areas of promotion? What would be the budget of this plan execution? Etc. Plus, you also estimate the ROI of this marketing strategy.