Writing a script is different than writing a novel.
This is a very true thing. Though you do write down actions, it is the dialogue that counts. You can have beautifully written action blurbs, but if you have boring dialogue, it won't be an interesting movie.
Now that we have that fact established, I will go over some tips.
1. Make all dialogue necessary.
This is true for a novel too, but for a screenplay, it is even more true. Dialogue takes screen time. You don't want a whole bunch of "Hi! How are you?" lines going around. It is okay to butt in the middle of a scene, as long as it will still make sense. Also, make it natural, yet witty.
2. You won't be able to share what the characters are thinking.
This is one of the hard parts of writing a screenplay. When writing a book, you can have the character thinking and feeling certain things. The reader knows this because it is clearly spelled out for them. But in a movie, it is up to the dialogue, actions, and actors to show this to them. Make sure the dialogue conveys emotion without somebody saying, "I am scared."
3. Make sure and tell the directors and actors everything that goes on "behind the scenes".
What I mean by this is that in the little "action blurbs" between the dialogue, what all the characters are feeling, how they are supposed to be talking, how they move, and what actions are taking place.
4. One page of properly formatted page of screenplay equals one minute of screen time.
This is important to remember so that you can calculate how many pages you need to make your screenplay.
The format of a screenplay is very different from a play script. If you have never seen one, I suggest you take a look at one here: http://www.imsdb.com At this website, there are a ton of scripts from real movies such at Narnia. I don't know how accurate the scripts are to the movies, but they provide good examples for what they look like.
1. Put "Fade In:" on the top left corner of the first page.
The first thing to put on the first page would be "Fade In:". You would also do this whenever a new scene has begun. This is directions for whoever edits the film.
2. At the beginning of each scene, after "Fade In:" you put something called a scene heading.
This is where tell the people reading the screenplay if the scene is inside or outside and where it is located. For outside, it should look something like this: Ext. Bob's House - Day. It could be night too, or something more specific such as "sunrise". For interior, it would look something like this: Int. Bob's Kitchen - Night. (Or day.)
3. After the Scene Heading, put action or introduce a character.
This depends on if you plan to set the scene without characters first. For example, if the movie takes place in New York City, your first shot might be an overview of NYC, possibly showing the Statue of Liberty. You would explain this, instead of introducing characters. Using this same scenario, here is what it would look like: In New York City, skyscrapers gleam in the sunlight. This might be the entire first scene. If it is, skip to step 5 and come back after you have started a new scene. If you plan to introduce a character, here is what you do. First, you describe them. When you mention their name for the first time, make sure it is in ALL CAPS. For example: AMY, a woman with fiery red hair in her mid twenties, walks on Broadway, her heels clacking against the pavement. Make sure you do this for every character. Now, not for all of the extras, unless one is important. Remember, not all characters who speak have to have a name. For example, you could call a baker who has one line and isn't called by name on screen, BAKER.
4. After you are finished with action, write the dialogue. This is where formatting gets a little bit tricky. Here is what a normal line in a play looks like:
Amy: (turns her head to Ray) I wish we didn't have to go home tomorrow.
Here is what this would look like in a screenplay (you might need to click on the picture to make it larger):
See? The dialogue is in the center with margins. The header to show who is speaking is always in CAPS, even if the label is THE BAKER.
5. After you finish writing your scene, make sure and put "Dissolve to:" at the end.
Put this at the very end of the scene, on the right side of the paper. Why is on the right side, I do not know. :)
6. Go back and do the steps over again until you have finished the script!
Proper Font, Spacing, etc.
Sizing of Letters: 12 pt. Font
Spacing of Lines: Based on what I have seen, it looks like between different parts, dialogue, action description, etc., there is a space between those lines. The alike parts are single spaced.
Action: Left Margin - 1.5 Right Margin - 1.0 Width - 6.0
Dialogue: Left Margin - 2.9 Right Margin - 2.3 Width - 3.3
I highly encourage you to look at a screenplay for yourself. Here is a link to the script for The Chronicles of Narnia: The Lion, The Witch, and the Wardrobe. Again, I haven't read it, so I don't know how accurate the script is to the movie, but it does provide a good example. http://www.imsdb.com/scripts/Chronicles-of-Narnia-The-Lion,-the-Witch-and-the-Wardrobe.html
- This provides a good diagram for format. http://www.writersstore.com/how-to-write-a-screenplay-a-guide-to-scriptwriting/
- Example Script http://www.imsdb.com/scripts/Chronicles-of-Narnia-The-Lion,-the-Witch-and-the-Wardrobe.html