If you are an untrained teacher, I would suggest starting with Betty Azar's grammar books and website (Welcome to AzarGrammar.com). I have a degree directly related to TESL and we had entire courses dedicated to writing lesson plans and teaching grammar, but nearly all the materials we used were course packages designed by the instructor. Teaching a grammar class is very similar to teaching other topics. Make sure you know your metalanguage (some students have amazing grammar knowledge), but don't overuse it during the lesson. What level?