Creativity can't be taught, but you can get better at aligning the circumstances that foster the greatest chances for creative expression. Creativity is not like a lightning strike, but more like something which bubbles up inside those who can create the right conditions for it to prosper.
Creative Exercises
Look at a picture. Think of 100 (or 50) words about the picture, write them down, then create a crazy story about the picture using all (or most) of the words.
Think for a half hour a day exclusively on one subject. At first, this might be very hard to do. You can start off by thinking about a single subject for five minutes a day, then increase the period daily until you reach a half hour. At first it is wise to practice this when alone, but eventually you should be able to do it even in the midst of distractions, such as when traveling to and from work.
Write a letter or speak for 15 minutes without using the words I, me, my and mine. Make it smooth and keep it interesting, so that someone reading or listening would never notice anything odd about it. This forces you to turn your mind outward, and give up the preoccupations and obsessions of your own life.
Have someone doodle a line for you, then challenge yourself to make a variety of cartoons based on that one line. Don't resort to drawing faces, though--those are usually too easy!
Take a familiar outline and challenge yourself to come up with drawings that could fit within that outline.
Combine ideas. Choose two random objects, and describe each one in detail. What does it look like? What is it used for? How is it made? Then substitute one object with the other objects description. How can I make object A feel like object B? Or do what object B does?
Keep a journal, describing everything you do and feel with metaphors. Each day, challenge yourself to come up with new metaphors. (After all, how many different ways can you symbolize brushing your teeth?) See How to Write a Metaphor.
Write a list of basic questions, such as 'What is your name?', 'Where are you from?', What did you do last Thursday?' Try to come up with at least 10 questions. The more you ask, the better! Whatever question comes to mind, write it down, even if it seems foolish. Answer the questions with song lyrics. (Try not to use the same song too often.)
Play word association games. It helps to have someone willing to play along, but if no one will, you can do this alone. If you're doing it solo, write down your beginning word and spend 10 minutes or so just saying the next word that comes to mind. Compare the beginning word to the final word. They should be pretty diverse. This loosens up your mind to allow free association of ideas.
See how long you can talk (and make sense!) without using a common word, like 'and','but', 'the' or 'that'.
Ask somebody to draw you a picture (ask him to try to make the picture nonsensical), and then write up a list of what the drawing may be/represent.
Try to tell to what each person you see resembles to you (by appearance or character). Don't push your thinking to a limit; it's not bad if someone is a carrot, or a table, just be sure of your choice.
If you have problems being creative, look inside yourself. Everyone is creative, but if you don't think you're 'good' enough to be creative, then chances are you won't be able to be as creative. Raise your self esteem and you'll find that it's a lot easier to be yourself.
Spend time around creative people. The most reliably creative people are children. Their imaginations aren't boxed in, and "mind merging" with them can remind you of what it's like to think outside the box.
Whenever you're challenged to create something, ask yourself: What's the most outrageous, preposterous, and nonsensical thing I can come up with?
