The first step in developing any instructional material, including PowerPoint, is to identify your learning objectives. In a sense we always have to begin with the end in mind. As Yogi Berra once said, "If you don't know where you are going, you will wind up somewhere else." In the case of education, the question is "Where are our students going? What should they know at the end of our course or our lecture." We also have to decide how we are going to measure their learning. In other words, what is the measurable outcome that we are expecting from the students?
Once you have identified the learning objectives, you are ready to consider the best means of helping students reach those objectives. What learning activity is the best way to help students understand, retain, and apply the new skill or knowledge? The answer may be a PowerPoint activity, or it may be another activity. Many times there will be better means than PowerPoint to engage students, to communicate an idea, or to illustrate a concept.