I love to kill two birds with one stone, and this activity fits that bill. I use this as a post-reading activity to include in a novel study or use with a short story. Choose a problem a character faced in the story. Discuss the problem and how the character solved it.
Then, have your students brainstorm other ways the problem could have been dealt with. This is where the lesson does double duty with a sneaky grammar lesson. You can teach modals of regret (could/should/would have done, etc.) without getting too personal with your students.
If your students are lower level, you may want to begin with a complete grammar lesson with scaffolded practice, such as worksheets, for the students to get some more focused practice.
Regular recycling of language and skills is vital to your students’ language development. To that end, you should periodically return to the basics including parts of speech.
Give the students several sentences and have them do one of the following: identify the part of speech of underlined words; circle (nouns/verbs/adjectives…); or add a word of the correct part of speech (fill in or multiple choice).
Scaffold with an example of the activity done correctly as well as examples of the part of speech being focused on, such as a list of 5-6 nouns they know.
For an example of this activity, using possessive pronouns, check this out. Of course, I love to use task cards for this activity, but I love task cards for just about everything.