Writing lesson plans

You need good written lesson plans, although there are not many hard and fast rules about layout:

They should always start with a purpose statement. It is good practice for the purpose to be what the student must be able to do at the end of the lesson. It can also be a question to focus attention on the goal.
Each lesson must have only one purpose.
Put notes in point form in fairly large print, so that you can easily glance down and see what to say. (If you write full prose, you will have to read it laboriously and lose eye contact with your students.)
The sequencing needs to work.
They need to conclude with some way of knowing whether or not the students achieved the purpose of the lesson.

Other things are simply recommendations:

Put a date on it so you know when you wrote it.
It works better to have as few pieces of paper as possible. If you can, it works better to see your whole lesson plan at one glance. (Besides, not many things are worse than shuffling bits of paper while teaching, especially if you have misplaced one.)
Many instructors like the landscape format so that notes can take the full width of the page. Besides, if you have a lesson book and you have two pages together, you can easily have a full A3 lesson plan in sight.
You might like to scribble your first lot of rough notes on paper. But it's a good idea to develop your notes with a word processor:

A computer print-out is usually easier to read than handwriting.
You can edit them easily without re-writing the whole thing, e.g. putting in things you forgot, improving the sequencing, changing layout.
Computer files are easy to save and keep organized.
Computer files are usually easier to find than bits of paper.

Print them out on paper. You will probably want to scribble extra notes on the page quickly, such as good ideas and changes you'd like to make for next time.
Collate your notes into a lesson book. It will make it easy to teach next time.

To get you started, here are three different kinds of lesson plan forms that you can alter to fit your particular situation and style: