Example:
Well, obviously the point of a formative assessment is to evaluate how the class is doing in regards to a specific course goal.
So the formative assessment is literally creating a situation where students can perform if not all, then some of the specific actions that will be required later in order to officially achieve the goal.
So this should vary for each course. This is 100% not the time for using cookie-cutter ideas. And as a teacher, you should be knowing what these goals are.
This isn't complicated.
In my class, one of the goals is accurate English pronunciation. So one formative assessment might be "Record the following words: beat, bit, bait, bet, bat." If all the words have a different vowel sound, then I know that student is on the right track. If some of the words have the same vowel sound, I know there might be some communication issues for that student down the line, and we've got to do something now, right now, to address the problem.
Once we've got it through everybody's brainium that these words have different vowel sounds, we can pick one of these vowel sounds, and start honing it, always in relation to the other vowel sounds, because speaking correctly is not about making specific sounds in an absolutely specific way, but rather, making sure that the differentiations between sounds are consistent. (For instance, although an English "laughed" and an American "laughed" may use a different vowel sounds, neither of them will ever sound like their respective accent's "left".)