For my friends who are starting grad school, preparing for quals, or just starting coursework again... the reading probably already looks pretty daunting. And it is. But here are a few tips on getting by.
First, Chad explains how to read scientific papers without reading every word. (Hint: it applies to HPS papers too!)
The first and most important point is to Know What You're Looking For. Different bits of information are found in different places and in different forms, so what you're looking for will determine where you look, and how you find it.
For example, if you're just trying to get a general sense of what a given paper is about, it's often enough to read only the introduction and conclusion. If you're just after a specific numerical result, it's probably in the abstract, or toward the end of the paper.
You should also be aware that what you're looking for may not be in the paper you're reading. If you want a sense of the context of a field, you're often looking for a reference to earlier work, possibly a review article. If you want the gory details of a measurement technique, you may very well be looking for some reference to an earlier or longer paper by the same group (a sentence of the form "using the method of [citation of earlier paper]"), or, even more annoyingly, some online supplement to the article you have.
(Of course, read the whole thing.)
Next, read Timothy Burke's How to Read in College.
Finally, check out John Bean's Helping Students Read Difficult Texts.
See also Jon's teaching tip on teaching critical reading in history.