Some things that might help...
How many distractions are around you when you're trying to read? TV on? Radio or ipod playing? Room mate chatting on the phone about beer pong? There's a reason that quiet libraries are popular during exams. Try as much as possible to eliminate things that can grab your attention, so that you can focus on what you're reading.
What else is going on in your head? Got 20 things to remember to do tomorrow? Worrying about how you're going to pay tuition next year? Should you ask out that cutie in your calculus class? Sometimes it can be nearly impossible to stay focussed. Something that helps me is making lists. I find if I write things down, I can "let go" of them mentally. Something else that helps is making constructive use of down time. I find it's easier to focus when I've taken the time to recharge.
Get adequate sleep.
Now for the actual reading. Sometimes it can help to have a goal. This can be anything from "I'm going to get through this chapter over the next two hours" to "I'm going to improve my understanding of time dilation" to "I'm going to take a break from reality for an hour and find out happened to Tyrion Lannister." When you set specific goals, you can tailor your reading process accordingly. For example if your goal is simply to understand something, it's often not necessary to toil over every little concept in the text, rather, to use the text to develop an outline in your own mind and then re-use it to develop details.
Vocabulary. Look words up that you don't understand. I know, this can be annoying. And when you're in university and reading in your native language, you often feel like you shouldn't have to look things up. But sometimes a simple google search can present a tonne of clarity.
Try talking about things you've read with others that are reading the same things. Sometimes trying to explain a concept (even if you're just talking to a wall) allows you to pinpoint specifically the areas that you don't understand.