The final P of the marketing mix is people. Develop the habit of thinking in terms of the people inside and outside of your business who are responsible for every element of your sales and marketing strategy and activities.
It's amazing how many entrepreneurs and businesspeople will work extremely hard to think through every element of the marketing strategy and the marketing mix, and then pay little attention to the fact that every single decision and policy has to be carried out by a specific person, in a specific way. Your ability to select, recruit, hire and retain the proper people, with the skills and abilities to do the job you need to have done, is more important than everything else put together.