Ideally, grade lesson plans should be orderly and sensible, but with enough room to include spontaneity and creativity. Anyone who has had to sit through a lesson plan that was rigid and tight, with absolutely no deviation from the tasks at hand, will know that this is a thoroughly unpleasant way to learn. Letting your students breathe a little is important in helping them learn and remember.
When it comes to constructing your plan, think about what the goal of each lesson is. Write this down, detailing any skills you intend to teach and include a brief description of the activity you have planned. Depending on how quickly your class progresses you may find it easiest to create your lesson plans on a weekly basis, always with the overall goal in mind. You will have a certain amount of time to cover a set amount of material so constructing lesson plans can help to ensure everything is running smoothly and on time.