Great question....I am a shodan in aikido and have been teaching for about a year. Well, a year, but maybe once or twice a month.
I like to review the history and terminology aspect of our curriculum prior to getting up in front of the class. When i was going through my kyu levels, i was frustrated at the fact that i had such a limited knowledge of aikido history as well as japanese martial history. I might throw out one or two terms so as to get the students into wanting to learn more.
As for an actual lesson plan...I dont really use one. Our Shihan has designed a monthly topic a while ago to focus our instructors and to sort of keep us on line so that kyus are prepared for testing. I think that is a really great idea. I try to stick to that as much as possible.
Now and then it might be a topic that i might not be all that versed, so then i have to borrow some of the knowledge of other sensei's that are present.
I thought that i read somewhere that O'sensei did not use a teaching plan at all. And when it came to him teaching techniques, he would just call up an Uke and leave to the uke to attack any way that he wanted. When i initially found that out, I tried to do is several times. But when i messed up several times, i elected back tothe "select an uke and tell him how to attack method"...Now that i am thinking about it more and more, i think that I am going to go back to having my uke attack the way that he wants. That approach illicits a number of different responses that aremore instinctual than prepared.
I hope that this wasn't too long.
I think that you have helped me think up another good thread question....