To pass a grammar lesson with a low standard, you need to touch on the meaning, form and pronunciation of the target language. You'll need to have a grasp of the language for that lesson, but you don't need an encyclopedic recall knowledge of all aspects of grammar. That's the reason books like this exist (highly recommended, by the way): most teachers need to double check before a lesson to make sure they're comprehensive in covering the TL.
The pre-course tasks will raise your language awareness and make you better at researching language, which will save you precious time once you're on the course.
http://www.amazon.com/Grammar-English-Language-Teachers-Parrott/dp/0521712041
I've found this book to be very useful and practical :)
I remember having to read this book when I did my last course: https://www.amazon.co.uk/Grammar-English-Language-Teachers-Parrott/dp/0521712041
This book helped me a ton when I was starting out. step by step instructions on teaching each grammar point
This book was my go to for improving my grammar teaching ability