So it sounds like you are just teaching a lesson and not planning your entire curriculum right now, is that correct?
You want to make sure youpick a topic that is appropriate for the age level of your students otherwise they will be bored. 12-15 year olds are probably not interested in finding a job. they don't really care about transportation. they are usually hungry so i'd go with food.
next thing you need to know is there level. then you will be able to pick a grammar point to teach them.
finally, you'll put your subject (food) and your grammar point together into a lesson.
Some things to make note of when making a lesson plan:
- time limits
- your goals for the lesson
- how will you present the material
- how will you practice the material
- how will you get the students to produce the material on their own (possibly in a game)
this should all be stuff your professor will have covered before they expect you to do it.