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.
Strategy _ similar to business strategy, marketing plan will capture strategies required to support your business strategy. For example if your business goal is to achieve 20% increase in sales, your marketing strategy would be to 1) introduce new product, 2) increase price for premium offerings, 3) recruit more distributors and offer commission scheme and so on. Strategy is king. When you can see your business in totality, I can assure you that you will find it easier to manoeuvre. Marketing plan is the place to address all these issues.