You will need to have a set of goals and expectations before you begin your preparation. Ideally, these should be written or typed and easily accessible. You will also need to gather supplies such as a pen and paper or a computer to organize your schedule.
With your goals and expectations in hand, you can begin planning your day. Setting up a consistent schedule is key to keeping control of the children, as they will know what to expect. Kids crave direction and consistency. Of course, there will be times that the schedule will just not work. Fighting to stay on schedule with one of these days will only cause headaches. Understanding that it is okay to be flexible with the schedule will make your life as a preschool teacher much easier.
You schedule should include set times (with flexibility of course) for each activity, snack time, and other breaks as necessary. I recommend having the activities that require more attention first. That may be reading time, math lessons, or some other focused activity. You can then rotate to a less focused, more "fun" activity.
The schedule you created will help you plan each day. Sit down with your schedule and your theme and decide what activities will reinforce your theme. Each activity, song, or craft should somehow tie into the theme or themes you have chosen. While not everything needs to be directly related to the theme, it is best to have some aspect of the theme as part of each segment.
The final step actually occurs after each day. Evaluate what worked and what didn't. Redesign your day based on the results. Of course, if the schedule had been working for a while and one day didn't, you may not need to change anything. That day might have just been a bad day.
Making small changes to the schedule at a time will allow you to evaluate what your group of children need and do best with. While some groups do not do well with some activities, such as circle time - reading a book, checking the calendar, and determining the weather - others may thrive on it. Only you can determine the best use of your schedule as you are the teacher.
So have fun with the schedule and figuring out what works for your class. Part of the joy of teaching is learning.