I have always had trouble writing character sketchs for the characters in my screenplays. I find it very difficult to explain a character in a few lines.
I would really appreciate some advice on how you guys go about making character sketches.
What you actually put into your screenplay is minimal as Rayw discussed. However, when I'm preparing to write, I like to flesh out my character(s) on a separate sheet of paper.
You can find books that give you character templates to fill out. In fact, if you're using CeltX, it has a very nice template that prompts you for creating character descriptions. But, really, you don't need to be that systematic. What I do is list some basic things about this character. Realize that this is for your use and doesn't go anywhere with the script. Casting is not the writer's call (unless s/he's also the director).
1. Appearance--build, height, weight, hair color, eye color, neat/disheveled, clean cut/unshaven, etc.
If I have an actor or see a character, I'll include the picture. THIS IS NOT a suggestion of who should be cast. It helps me to be able to visualize the character in scenes. Do they have moles? tattoos?
2. Behaviors--Do they have quirks? Are they superstitious? Do they need to stop when passing a mirror to check their appearance? (More often guys than girls!) Do they speak with an accent or dialect? Are they alpha's? Are they neat or slobs?
3. What was his/her family like? This is a tricky one since you may need to do some research. Don't just use your own family as the model. Here, reading biographies or novels can broaden your options. Families shape our values and relationships. And I can guarantee that even if not directly discussed in the script, it will help you in writing the relationships.
4. What are their current relationships--home, work, community? Do this outside of the scene writing. Is he generally happy at work? Is her relationship with her boyfriend strained? Is the neighbor unduly nosey?
5. What are their strengths? weaknesses? These can be physical, intellectual and emotional. In drama, you want to have your story line challenge the strengths to the point of failure and have them overcome their weakness(es) to find a new strength. You don't have to worry about that at this point, but you want to really make this a 'real' person in your mind. Then your unconscious can kick in later.
6. What is their 'catch phrase'? This isn't so much something the character says but it's their guiding philosophy. When I get stuck writing, I'll go back to my character's 'catch phrase' and see how s/he would apply it to get out of their situation.
7. "The Vacation" -- A friend suggested this and I really like it. Imagine you were on vacation with your character, what would you and s/he chat about? What are their dreams? Are they outgoing or introverted? Would you like this person to hang with?
In all you may have six paragraphs or a page or more. Now you don't have to do this for every character. There are your main characters (protagonist and antagonist). They need it. You have your supporting characters (mentors, friends, minor adversaries) and it helps to define them also but perhaps not to the same degree. Your "extras", the characters who though they speak really are there only to move along a scene, don't need it. If the hero stops and talks to a merchant, you don't need to detail the merchant if that's his one scene. If the merchant plays a continuing role, you might need to do a little work.
In your script, the relationships are the most critical area. As a writer, you are essentially 'acting' all the roles. So it's very important to make sure your characters don't all act or sound like you. By taking the extra effort of making them independent, you make that chore easier. And having it written, you can go back and ground yourself when needed. For TV series, you will always have the 'series bible' which details the characters, locations, etc. for continuity among the many writers who contribute.
Echoing Rayw, these are only for the writer's eyes. What actually gets written into the script will be what is absolutely essential. Since you can't see what's in a character's head, we need to write what's being felt or thought visually. And when you have your character sheet, that helps. ("Yeah, this guy is nervous. I'll make sure to write he's fidgeting with a coin or something.")
Hope that helps. Do check out CeltX's character sheet if you are using it for your screenwriting.