What literary techniques does J.K. Rowling use in Harry Potter and the Sorcerer's Stone?
Three literary techniques that Rowling uses very successfully to pull us into her imaginative world are humor, contrast, and imagery.
The novel's opening, which highlights the exaggerated stupidity, meanness, and conventionality of the Muggle Dursleys, as well as their abuse of Harry Potter, brings us into the story, makes us laugh, and builds sympathy for Harry. We are soon rooting for him to succeed against the hot-tempered Vernon, petty-minded Petunia, and bullying, spoiled brat Dudley. This humor continues, if in a more dead-pan way, as Harry attends Hogwarts. For example:
What happened down in the dungeons between you and Professor Quirrell is a complete secret, so, naturally the whole school knows.
This light-hearted approach to a serious theme keeps the book from becoming preachy and unbearable.
Rowling also contrasts the dull, pedestrian, unimaginative Muggle world with the magic and enchantment of the wizarding world. She contrasts Harry's low status in the Muggle world, where he is treated with contempt by his adoptive family, with his high status in the wizard world. The two worlds are opposites of each other, and with such a stark contrast, who wouldn't want to leave the Muggles behind? The following passage contrasts Harry's two very different positions in the two worlds:
A breeze ruffled the neat hedges of Privet Drive, which lay silent and tidy under the inky sky, the very last place you would expect astonishing things to happen. Harry Potter rolled over inside his blankets without waking up. One small hand closed on the letter beside him and he slept on, not knowing he was special, not knowing he was famous, not knowing he would be woken in a few hours' time by Mrs. Dursley's scream ...
Most of all, in my opinion, Rowling is superb at using imagery—which is description using the five senses of sight, sound, smell, taste, and touch—to paint a convincing and compelling picture of her fantasy world. You really feel that you are there: that this is a real place coexisting with our more mundane world. The following example shows both imagery and Rowling's trademark humor, as Neville tells how he first performed magic:
Great Uncle Algie came round for dinner, and he was hanging me out of an upstairs window by the ankles when my Great Auntie Enid offered him a meringue and he accidentally let go. But I bounced—all the way down the garden and into the road. They were all really pleased, Gran was crying, she was so happy.
If you want to be very detailed in this answer, as you read you should search for examples of figurative language (similes and metaphors). Rowling uses several in all the Harry Potter books.
On a broader scale, however, the most noteworthy literary elements for analysis in any of the Harry Potter books are going to be things like point-of-view, setting(s), symbolism (in objects, characters, and the many symbols--used as labels--found throughout Hogwarts), and foreshadowing.
Symbolism is probably the largest and easiest element to look at. This book is the first in what becomes an entire series of fantasy books that encorporate very unique story lines with very traditional elements of good vs. evil, magic, mystery, and fantasy. Everything in Harry's world is symbolic of something else. Consider for example, the four houses at Hogwarts, the symbols associated with each, and the traditional associations that come with each. Consider the difference in symbols used for good vs. evil and the way each character is associated with either an animal, natural element, or some other identifying object that gives insight into his or her personality.
Additionally, you could analyze the above techniques through one of the main themes of the book. Finally, because the story is written at about a 5th grade level, you could look at the elements of foreshadowing throughout the story as the mystery (and Harry's historical back-story) are slowly revealed.