As you move through school, the expectation is that you will have more and more information upon which to draw in writing essays
and that your ability to think creatively and analytically will increase. To foster development in both of these areas -- knowledge and critical thinking --
read and write every day.
Read a variety of things, utilizing the wide variety of material available on the web but also looking into printed publications such as magazines, newspapers, and -- especially -- books. Keep a journal in which you reflect each day upon what you have read. Over time, you will find that your "imagination" improves naturally.
Simone, EssayForum.com