Most writing exercises involve one writing by themselves, and some people are not motivated enough to work at these exercises to improve. If he or she wishes to improve his writing, but he can't keep his focus or gets bored too easily, there is something else you can do.
I like to call it "Joint Writing." This exercise is when you and at least one other person get together and write a piece of literature together by taking turns. The piece can be fictional or nonfictional, depending on your mutual interests. Each person takes turns and adds on to his partner's response, each from a difference perspective.
This exercise helps with character development, for your responses would be in response to your partner's. Your partner would have his own perspective and his own "character" that responds to your replies. (This is also known as a form of "role-playing.")
What you do to complete this enjoyable, simple exercise is very easy:
- Get a partner (or more).
- You're going to need at least one other person to complete the exercise. Having a partner keeps you motivated and interested.
- Come up with an idea.
- You'll need an idea to spark up the piece in which you and your partner will write.
- Keep it unpredictable, if possible.
- If you and your partner keep to a mundane topic that both of you expect certain responses to, neither of you will want to continue when you've barely gotten half-way through the exercise. Keep it interesting.
- React, react, react!
- The point is to improve your writing skill by trying to use your "character" to respond to a situation you'd never think of yourself. If your partner comes up with a situation, then react! In a chain of events, your partner will reply to your response, and soon you'll have a very interesting plot going; one you may have never even thought of!

To complete the exercise, you only need three things: something with which to write (pencil and paper, a computer, etc.), a partner, and an idea. All of these things put together give you the opportunity to improve your writing and ability to develop characters.