Question the textbook sometimes. Not to be difficult, but to make sure the thinking in your head is yours.

Accepting something because it was printed is efficient and leaves you unable to tell which of your beliefs you ever examined. The point of asking is not that the book is wrong, since most of the time it is not. The point is that the checking is what turns information into something you actually understand.

Take one claim this week that you have always accepted and follow it back to where it came from. Ask how it is known, not only what it says. Even when you end up agreeing completely, the belief is yours afterwards in a way it was not before.