If we start from the beginning, when Harry has a nightmare. Or rather, a sighting. The book states that he can see Voldemort and Wormtail discussing plans. In the movie, however, Barty Crouch Jr. is also present.
In the book, Harry had this nightmare while still at Dursley’s, but in the movie we see him waking up at the Burrow.
After the Quidditch World Cup match there is a Death Eater attack. The Death Eaters in the book were much more evil than the ones in the movie. In the book, they attacked the fans while they were all already sleeping. In the movie, they attacked them while they were still celebrating.
The Dark Mark that was cast by Barty Crouch Jr. in the movie, was cast as a call sign, to tell everybody that the Death Eaters are responsible for the attack. The book says that the person casting the mark was unknown at the time and that the mark was used to scare away the Death Eaters for disloyalty.
When Harry is competing in the tournament and has to grab the golden egg, the book says that he does so by using his flying skill on a broom. The movie shows that Harry has a lot of trouble getting to the egg and he has to leave the arena and it is not until the dragon crashes into the bridge that Harry can go ahead and pick up the golden egg.
Guess who does not appear in the movie? Yep, you guessed it; Peeves. As we are used to by now, he likes to cause trouble and surely enough, he was accused of stealing Harry’s golden egg, while he was trying to work out the clue. Too bad we did not see him in action.
The second task later began on the shore of the lake. The movie shows them all standing on a platform built in the middle of the water.
When they are all running in the maze, Harry gets stuck by the roots and Cedric is there to save him. In the movie, the roles are reversed and Harry saves Cedric. There seems to be a lot of confusion between these two guys, because Harry asks Cedric where they are after they are ported to the graveyard. The movie, again, reversed the roles.
When Voldemort is reborn in the movie, his eyes are blue. The book sticks with the initial description of Voldemort and has him come out with red eyes.
This is all. As always, I have included the ones that I feel are the most interesting.
Until next time. Mischief managed.