This is the rule 6 of Analytical reading.

First, Looks for places in the book you don't understand.

Ways to sink in a proposition (that is, to Think critically):

Reciprocal writing practice: Highlight key sentences in your writing.

References

‣ You must also mull things over, compare what I say with your own experiences, talk with others, and make some of the points part of your way of doing things.