Guide _ in a marketing you will think, record and document all your ideas, products and services offering, price, distribution channel, programs, sales direction, customer segment and so on. I have experienced whereby I suddenly realized that my business is not going on the right direction because I didn't follow my marketing plan. Have you experienced that? Or perhaps you suddenly realized that the thing you do know supposed to be done many months ago because you forgot about it? And you forgot because you don't jot it down and plan for it? This is what I mean that marketing plan as a guide. I cover this in my Marketing Plan Breakthrough S6PEC.
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.