This article is intended for composers and music producers who want to create content for moving images such as: video games, silent films, animated films, feature films, documentaries, fiction films, children's films, artistic films (for museums or competitions), series of television, etc.
Steps

Step 1. Immerse yourself
Start by watching the movie once to discover the story, then watch it again and you will start to see different things, and to get into the rhythm of the film, the video editing, other details, and the climax (a bit like a symphony).

Step 2. Live the product
Keep the movie playing in the background while you do other things (work on the computer, send emails, etc). Your brain will start to get more used to the movie. This is much more efficient than we think.

Step 3. Watch the movie without sound
Play it again and mute the sound completely - a new dimension will be revealed. In fact, it can tell you more than sound. You will start to see more details or you will notice other things, if it is very quiet or very fast. They will also highlight the recording style and video editing more. Your brain won't be distracted by sound (our ears are much more sensitive than our eyes), so this will free up space in your mind to focus on images.

Step 4. Select the instruments and atmosphere
Instruments are chosen depending on the atmosphere. They can be instruments that you haven't used before. Hopefully at this point the video will tell you what it needs.

Step 5. Keep up with the video editing
Video editing can be fast or slow. Make sure you get the "beat" of the movie. The rhythm can vary a lot (you can see an example in this video created with European music for a film festival. Http://www.youtube.com/watch?v=IY48XFSFQW4). Pace and speed continue to change throughout the video and it is important to adapt to that.
Step 6. Follow the story, what happens in each frame
Watch the video to understand what it means to follow the story in every frame (every second):
This is not mandatory; in this case, the music was for a silent movie, so there was no other sound in the movie, allowing the entire sound space to be used. Most of the time, the music you will compose will go along with other sounds (actors, voices, ambient sounds, etc)

Step 7. Follow the emotions in the movie
Composing music for movies is about emotions. Make sure you really understand the emotion the producer is trying to emulate and stick with it. The emotion can vary from one second to the next. People have hundreds of emotions every day, so make sure your music evokes the right feeling; and make sure it succeeds in emulating that sentiment (even if you listen to it without seeing the images).

Step 8. Don't ask for comments
Comments can be a double-edged sword. If you are really immersed in your creative process, comments may or may not be helpful. You should be confident enough to know exactly where you want to go in terms of intention and emotion, even when you don't have a clue as to what instruments will get you there. You can choose to compose surrounded by people or completely away. Both options can be helpful.

Step 9. Dive in
Let the movie take over. Like an actor who suddenly becomes his character, and lives, breathes, eats, sleeps and talks like his character, the images will inspire you to do the rest.