You must know your competition in and out. Keep your friends close, but keep your competitors closer. You need to know all the things that you learned about your customers except fill in the blank for each competitor on all of those above items. Learn how you are the same/ different. Learn the similarities/differences about each product and service you offer. Learn how they sell or promote their products /services.
Therefore, a marketing plan, according to Kotler, is a "written document, which includes the objectives, strategies and action plans regarding the elements of the marketing mix which facilitate and enable compliance with the strategy dictated at the corporate level".