When Wells wrote the book in 1898 there were no planes, vehicles were mainly horses, and space travel was far off in the future. When the movie was produced in 1953 the world was a much different place. The original plot is the same in the novel and the movie. The Martians were known to have come from space. The people thought they were meteors coming down.
In the novel the story takes place in England. In the film version the story takes place in the United States in California. Also, the time period was much different. In the movie the time period is the 1950's. In the novel the time period is set in the late 1800's.
The main characters are also very different. In the novel the narrator is the main character. He is married and he is telling the story to his brothers in the first half of the book. Later in the book he tells his own story. The novel never reveals the narrator's name.
In the movie the main character is a scientist named Dr. Forrester, he also happens to be single. In the beginning of the film he meets a woman and she stays with him most of the film. In the movie only one story is told, the story from Dr. Forrester's perspective.
The film and the movie start out the same. Cylinders fall from the sky and they are thought to be meteors. In the novel the Martian machines walk on t tripod legs. "Hundred feet high. Three legs and a body like luminium, with a mighty great head in the hood."
In the movie they turn out to be flying machines. The machines have basically the same type of weapon; the heat ray does not seem to change from the book to the movie. "It was sweeping round swiftly and steadily, this flaming death."
The book talks more about what the Martians are...