Lesson planning is the activity which the teacher performs before the actual lesson takes place. A lesson plan is a detailed description of the instructional strategies and learning activities to be performed during the teaching/learning process. This important preparation involves the following:

Identification of learning as well as teaching objectives, activities and tasks to be undertaken by both the learners and the instructor. 
Sequencing of these activities and tasks.
Determining appropriate instruction aids, methods and references.
Deciding the proper organisation and or management of the learning resource available, environment and activities.
Determining evaluation process i.e. how the learner shall be deemed to have acquired the desired chance of behaviour or mastery of content and/or skills.
The importance of a lesson plan is that it enables the teacher to read ahead in order to enrich the content area and skill to be taught, to have confidence during the actual teaching/learning process and to logically present the content standards for effective learning.