If you have ever been surprised by what your ESL students don't know, you are not alone.
I have been in that situation many times.
When you get a new group of ESL students--or even a group you have had for a while--finding out what your students know and don't know is a good place to start.
Once you know in what areas your students struggle, you can prioritize how you spend your time.
Otherwise, you run the risk of putting the cart before the horse.
In my case:
The cart = Writing a Story
The Horse = The Past Tense