Planning can be difficult when you are dealing with preschoolers, but the more accustomed you and your students are with the plan the easier it is in the long run. Changing the routine can confuse students. This is especially true for students who leave early or come only two or three times a week. When selecting activities and songs that you do every day, be firm with your choice and stick with it.
Lesson plans and activities take longer with preschoolers. Their shorter attention spans and different learning styles will prevent all of them from catching on to what you're teaching quickly. When you select an activity, assume it will take longer. This will prevent you from rushing through a lesson plan and not having enough time to transition from one activity to the next.
If you are fortunate enough to have a teacher's assistant, take advantage of it. Have your teacher's assistant help children who are behind catch up while you teach a new lesson to the other students. You can print extra worksheets for her to go over with students or have her review misspelled words or colors with the students.
Understanding that preschoolers are unpredictable will prevent your from being frustrated. If you are not frustrated, you can focus on the task at hand. Address behavior issues as they happen, but do not spend a lot of time reprimanding the child. Make note of the incident and speak to the parents when they come to pick up their students. Letting them handle the bulk of the disciplining will take that responsibility off of you and allow you to focus on your other students.