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.
Gathering information: this stage is based on the concept of marketing audit. After performing the audit of the macro_environment by analyzing the STEP factors (social, technologic, economic and politic), we should turn the focus upon the immediate extern environment (the micro_environment) and analyze the competitive environment, the costs and the market. Finally, we will conclude with the SWOT analysis, by this way we will have a general view upon the internal environment compared to the external one. The SWOT analysis combine the two perspectives, from the inside and from the outside, because the Strengths and the Weaknesses are internal issues of an organization, while the Opportunities and Threads come from the outside.