Reading The Turn of the Screw, I found James's 1898 novella to be an intriguing tale of a young governess' internal struggle to explain the strange happenings around her. When I watched Jack Clayton's 1961 film adaptation, The Innocents I felt that this sense of mystery and intrigue was lost. So, if I were to film a move based on this book, there are a few things I would do differently.
First, I think the casting of the children is important. In the first chapter of James's novella, the governess describes young Flora (portrayed by Pamela Franklin in The Innocents) as on "angelic beauty" and says she has "the deep, sweet serenity indeed of one of Raphael's holy infants." The dark-haired little girl with the evil glint in her eye playing with dead insects in the film does not look remotely angelic. In James's novella, Miles (portrayed by Martin Stephens in Clayton's film) also appears sweet and innocent. The governess recounts that when she first sees him "on the instant, without and within, in the great glow of freshness, the same positive fragrance of purity in which I had from the first moment seen his little sister." She says in James' third chapter that he has an "indescribable little air of knowing nothing in the world but love." Once again the Miles in the movie looks, from the very start, as a child with a definite air of darkness and evil surrounding him, not an air of love. Thus, casting more innocent-looking children would be a first step in adapting the novella to film again. I would certainly not have them playing with dead insects either.
Secondly, the unseen tends to make us far more uneasy than what can be seen. In order to capture the same sort of unsettling suspense that James creates, it would be more effective to not actually see the ghosts. With good acting, we do not actually have to see what the character sees to understand his or her emotional response. The fact that James lets us decide for ourselves whether the ghosts are real is an important element of the mystery. It might be possible to show flashes of what might be a ghost and still create the same type of mystery. The ghosts should not be blatantly revealed to the audience from the start, though.
Finally, I would take out those awful open-mouth kisses between the governess and Miles in Clayton's movie. Those certainly never occur in James's novella, and I am not sure why Clayton felt the need to include them. These disturbing scenes are not something that I would want imprinted upon the minds of viewers.