When summarizing take the main points from the author and put them into your own words. Avoid including your own thoughts and opinions.
For example, if you were to summarize the following excerpt from an online movie review of Harry Potter and the Half-Blood Prince:
"Surgically adapted by Steve Kloves, who has written all the screenplays save for No. 5, “The Half-Blood Prince” was to be the penultimate film, the corollary to the J. K. Rowling book. Instead, the concluding volume, “Harry Potter and the Deathly Hallows,” has been deemed hefty enough by Warner Brothers — 784 hardcover pages, 2.4 pounds shipping weight, a fight to the death — to be split into two movies that will hit in late 2010 and summer 2011. Considering that the take for Harry Potter and His Big Pot of Cinematic Gold now totals almost $4.5 billion in international box office, the studio’s reluctance to embrace the end is touchingly obvious."
(MANOHLA DARGIS The New York Times)
You might write this summary:
Warner Brothers will split the final installment of the Harry Potter series into two separate motion pictures. They're set to be released in late 2010 and summer 2011. Given the previous success of films in the Potter series, Warner Brothers hopes to milk the series for all it's worth (Dargis).