In the book, Tolkien had dominated battle scenes with only male characters to be able to have the knowledge to add more detail into the scenes such as blood and gore. This meant that the book had to be rewritten for the screen play to involve more female characters to save controversy between genders.
Characters within the book had to be cut out due to parts of the book being rewritten or even completely taken out as they did not move the story along.
Exposition scenes were difficult to do, they were used to move the story along. The reason they were so difficult was because they had to write a whole scene that never happened in the book to carry the story on, due to the earlier removal of specific scenes they had to add more exposition scenes to explain the story, totalling up to 4 pages of exposition before the film even starts. (In the film, the exposition scenes at the start were where the ring bearer looses his finger and the ring to an earlier king).
A lot of the creation of this film was made in a hotel room, writers and actors were surrounded by notes, locked in hotel rooms, 15 months of shooting was written. The script was rewritten constantly for the whole period of the making of Lord of The Rings. Actors were asked to input ideas about what made them laugh, what they thought the character would do (eg. Frodo playing/handling the ring). Liv Tyler brought in the idea of no female characters and the issues with having no main female characters, this made the writers having to rewrite a lot of the script to fit in with the female population. Gender was a massive issue when creating the movie to LOTR as it was originally written with no leading female characters, to fit a modern audience they had to add female characters to have a wider audience and more contemporary for todays viewers.