By the same principle, read the first chapter (approximately) of next term's textbook to get a good summary of what you need to learn now. You can continue this method all the way to research monographs, as long as you can tell what books are at the next level (and if there is a next level, but that's where the papers come in). Of course, you only get an overview, but sometimes that's all that you need.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.