If you are waiting to do a Module, the more you can read, the better.
All of the Modules overlap, so things you read for Module One will be useful in Two and Three. Some of the reading for Three is more specialist and doesn’t feed back quite so directly into One or Two.
Reading for Modules Two and Three once you are actually doing them is reading so you can write (background assignments or sections of your extended assignment) and that direct relationship should make your approach quite focused.
If you are trying to extend your ELT background knowledge for Module One, or reading to prepare for Module Two or Three (as you can’t start assignments properly until you have met groups) you will be reading in a more general way. You need to do something with that information (actively do something) or it will disappear again before you know it. There are some ideas about that on the ‘How to read the things you find’ page.