I myself am a motormouth; I can talk about anything almost endlessly. So for those of you less congenitally verbose, here are two suggestions.
First, take the given statement, and quickly generate one or two mirror-images or opposites. Writing about each one will take up multiple sentences. If the statement is, "No one accomplishes anything important without persistence," then you add "Many people accomplish important things when they do persist" and "Many people accomplish trivial things when they give up quickly." You should also consider the opposite: whether anyone has accomplished something important quickly and easily.
Second, come into the exam room knowing seven stories that you can tweak to illustrate most situations. Glean these stories from your experience, from history, or from fiction--those novels and plays assigned in your English class. If you want to index these seven stories, I recommend generating them around either the traditional Seven Deadly Sins or the Seven Virtues:
Stories that illustrate the effects of Pride, Envy, Hatred, Greed, Lust (careful on this one), Sloth, and Gluttony.
Stories that illustrate the effects of Faith, Hope, Charity, Justice, Fortitude (persistence), Prudence and Temperance (look it up).
These stories are easy to remember and will fill up your exam page.
They may also make you an even more interesting person.
