The e_marketing plan is built exactly on the same principles as the classical plan. There is no different approach, but there might be some formal differences given by the uniqueness of the internet environment. Many of these differences come from the necessity to ensure a high rate of responsiveness from the customers, since the e_world is moving faster and requires faster reaction from its companies, compared to the traditional offline marketplace.
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.