Role of the writer

What changes had to be made from the original book to the screen play?

Making larger roles for the female characters in the film

giving them more words to their parts of the script to give them a larger role because they could expand more on the females scenes in the movies and give them more actions possibly in fight scenes they could take part in 

giving female characters more things to do in a film - the character Arwen in the film had different roles in the films as both Lady of Rivendell, Queen of the Reunited Kingdom 

Taking out (omitting) certain characters in the film look at this site for help

Tom Bombadil was  the character taken out from the films because he wasn't needed.

they needed to take certain characters out so it makes it more interesting over time and they wasn't relevant in the story 

Writing an exposition (what has happened before the film starts) scene for the beginning of the film

a battle happened before the story started and creating 4 rings and then they fight for them

the lord of the rings has a montage at the start of the film explaining what the movie is about and what is going to happen 

Working with the actors as characters to create some parts of the script.