I'd like to enthusiastically reinforce celeriko's comment above. It seems that students often don't pick up on the fact that really "juicing" something basic is what allows for fluent thought about later mathematics. We should build assignments that aim to teach students to slow down and read carefully to process what is being said. We should encourage them to work out simple examples and to modify hypotheses, to find easier questions and harder ones. I suggest that for assignments like these it should be made very clear that the point is not to get an answer but to build a solid mental picture that one can fluently think and talk about.
Here is a quote from Bill Thurston:
"I was really amazed by my first encounters with serious mathematics textbooks. I was very interested and impressed by the quality of the reasoning, but it was quite hard to stay alert and focused. After a few experiences of reading a few pages only to discover that I really had no idea what I’d just read, I learned to drink lots of coffee, slow way down, and accept that I needed to read these books at 1/10th or 1/50th standard reading speed, pay attention to every single word and backtrack to look up all the obscure numbers of equations and theorems in order to follow the arguments."
—Bill Thurston, from the foreword to Teichmüller Theory and Applications to Geometry, Topology, and Dynamics