Jane Austen's Pride and Prejudice is one of my favorite books, but it's also a difficult read, so good for you for improving your English by reading such a challenging book! Here are a couple of tips that will hopefully help you read this book more quickly and efficiently:
- You should be aware that many readers who grow up speaking English have a hard time with Austen's prose. Published in the early 1800s, Austen employs an ornate, lofty, witty style that, while finely crafted, often proves to be challenging and even baffling for modern readers. Native English speakers should expect to read more slowly at first, so keep in mind that you don't have to zoom through this book extremely quickly. Also, don't think you have to spend a lot of time gleaning every single detail from the text. Rather, try to get the main points and move on, as there's no need to spend hours agonizing over outdated English.
- To read a book faster, it's often helpful to know the basics beforehand. Since you've already seen the movie, I won't explain the plot, but I will explain some of the book's primary stylistic points and themes. First of all, you should know that, while there is definitely earnestness in the story, Prejudice is also largely satirical. Austen was a deft commenter on the upper classes, and much of her work playfully, ironically, and subtly satirizes the traditions and lifestyles of England's richest classes. Additionally, the novel can be seen as feminist, as it primarily explores the social situation of women and especially comments on the ways in which women are forced to rely on men for financial and social support.
- Much of Austen's story is advanced through dialogue, and the author often comments on and explains what happens in the dialogue. So if you're having trouble understanding the written dialogue in the story, don't waste too much time on it; instead, proceed as best you can to the moments in which Austen offers some explanation of events in prose, as these might help you quickly resolve any lingering confusions.
Good luck! Hopefully those tips help. If you're still having trouble understanding the novel, I'd take a look at some of the Prejudice adaptations that have come out for television; many of them are quite good, and they include more of the novel than the most recent movie does.