How do you prepare for a journal club without summarizing the entire paper?

Whenever I prepare for journal club, I end up making a long summary that repeats most of the paper.
Then the actual discussion focuses on things I barely considered: whether the method answered the research question, what assumptions were made, what alternative explanations exist and which limitations actually matter.
I understand the paper, but I’m not preparing for the discussion part.
What questions do you use to move from “I read it” to “I can critique it”?