One hallmark of adult ESL (in not-for-college-credit settings especially, to my knowledge) is that all of the students are at remarkably different levels. For example, some of my students have been in America for decades, while some arrived about a month ago. Some of them have had 24 years of formal education in their lives (not necessarily in English, of course). Some have had no formal education at all before taking ESL.
The next unit we’ll be studying in the text hits on the following grammar points: can, have to, simple present, simple continuous, and adverbs of frequency, and expressing time. That’s a lot.
For a few of my students, all of the grammar listed above would be a great review. To other students, some of the grammar would be review, and some will be new. And to a few, it would be basically all new structures to learn.
So my planning first of all consists of deciding which points to focus on so that everyone actually learns something usable. And whatever material that turns out to be, my job is not just to introduce it in small, logically-sequenced bits with plenty of opportunities for practice, but also to keep the more advanced students interested and learning while the others catch up, or at least make progress.