Yes is the short answer. Any time you are planing on generating money, you should have a plan. No plan means no real focus. There may be some 1/1000 percent of a chance you will succeed, but I haven't met them yet. If you have already started and have generated an income, record how. Doing so will give you material for use in expanding your business faster.
Will my target audience realistically buy this now, or at a different time? Be sensitive to sales cycles and seasons. Maybe you should avoid holidays (when people are away from their computers, like July 4 in the U.S.) or maybe you should target holidays (like the day after Thanksgiving), but know the difference. Again, know your audience. Plan your content accordingly.
The moment you step into the world of affiliate marketing, the key skill needed to make you succeed is expertise in digital marketing. While it may take some time for you to figure out whether email marketing works for you, or is it SEO, it is a good idea to begin by knowing all fields of digital marketing and then deep diving into one particular subject. You will learn about topics including Facebook Marketing, Twitter Advertising, Quora Marketing, Google Adwords, Google Analytics and even EMail Marketing, SEO Fundamentals as well as WordPress.