First things first, it might be worth checking if there is a specific lesson plan format that you need to follow. Some schools, colleges and universities have a standardised format to follow as this makes it easier for another teacher to use if you are unexpectedly away from work. While there are many different formats you can use for a lesson plan, most contain the same core elements. The title and time of the lesson are basic pieces of information and a list of required materials ensures no essentials are missed out.
Once you have finished your plans, you will find that your class runs much smoother than it would without it. For example, your students will enjoy the luxury of the daily routine and the security of knowing that their teacher will know exactly what the plan is on a day to day basis. Should a delay occur, such as a classroom discussion tangent or a school cancellation, you will nevertheless have enough time to reschedule various events. Writing plans are also useful in that if you plan to take any field trips, you will be able to prepare for these events ahead of time.