Characters are the beating heart of playwriting.  Without them you have an op-ed piece or a history lesson.  One of the primary skills expected of a playwright is the ability to create good characters.  How does a playwright go about doing this?  TRY TO TELL THE TRUTH.  I think that's the cardinal rule. What would these people really do and really say?  That rules out what characters in other writers' plays and movies would do and say because the work wouldn't be coming from you.  It's just reporting what other people have done.  Of course there are exceptions.  There are exceptions to everything in writing a play.  Tom Stoppard wrote a whole original play about characters in another play (Rosencrantz and Guildenstern Are Dead), as an example, but he used what Shakespeare had created as a jumping off point for his own thought processes.  

The obvious way to write good characters is to write about yourself and/or people you know very well - family members, old friends, teachers, the like.  Arthur Miller's uncle was, apparently, the basis for Willy Loman, and Tennessee Williams' mother inspired Amanda Wingfield.  There are countless examples of this.  I've certainly done it, as have most of my colleagues.  Writing about people you know doesn't mean you just remember and write down.  You need to think first - long and hard, about who this character really is.  Sure, it's your Aunt Rose or whoever, but filtered through you.  You can't know what Aunt Rose felt, just what she did and said and how she interacted with other people.  You have to figure out why she said or did it and what she meant.  I don't believe people usually say what they mean.  More often than not they  just say what they say.  It's what they're feeling when they say it that counts and that's where the thinking comes in.  You owe it to your director and your actors to justify everything you write.  Often an actor will ask you "Why am I doing this?"  "Why am I saying this?"  and you'd better have an answer that makes sense to you.  Don't give them bullshit because that's what will come out in the playing.  I usually write myself notes about characters I'm trying to create. What do they like?  What do they not like?  What would they change about themselves?  etc.  Of course I'm making it all up, but if it seems real to me I can write interchanges and eventually scenes.

A playwright needs a good ear.  What were Mom's exact words when she told you that Dad died?  What did your girlfriend actually say when she ditched you?  The trap here is to come up with generic reactions and not dig for the real ones.  Also it helps to be snoopy.  I always enjoy sitting in airports and figuring out why people are traveling together and how they feel about one another. You can tell a lot that way.  Once I was on a 7am 20 minute flight and the two men across the aisle drank two glasses of champagne each in that short amount of time.  I assumed they had to gear up for where they were going.  They didn't look like businessmen, no briefcases, etc.  So I started imagining what they were going to do when we got to Raleigh/Durham.  I don't know, of course, but I've used those two in my work several times and in several situations.

Here's where the ear really comes in handy.  What if you're writing about famous people or historical figures.  To cite Arthur Miller again, he wasn't around in seventeenth-century Salem, Massachusetts so how could he possibly know what those people were really like?  I would guess that he read up on the period and he became familiar with details of daily life.  But what did they sound like?  That’s where his ear started to work for him.  He imagined and then created a way of speaking based on what?  I don't know,but it works. I believe this is the way those people would've sounded.  And as for their behavior, well, they were people, so they had to think and feel and act like people do and always did.  It's a bit of a sleight of hand, I think, combining imagination, research, a good ear and who-knows-what?

Not easy?  Of course not.  But it's fun to write characters. It's fun to dig and poke around in your mind and come up with something your eighth-grade gym teacher said once.  Who knows where your mind will go when you let it roam?  Plotting a play is hard work for me.  So is the overall structure.  But the characters and the beauty part -- I hope all of you find them as rewarding as I do.