Check that you have developed all of the information required of you. Otherwise, your conclusion could fall short in that you aren't adequately recapping all of the information that you need to. Depending on the professor grading it, you could become a victim of double jeopardy; not only will the body of your essay get penalized, but your conclusion could lose points as well.
Analyze what you have thus far. Put yourself in the shoes of the reader and ask yourself what needs to be said to finish things up in a clear, concise way. Pretend that you are reading a completed essay, sans the conclusion. What things need to be addressed in order to wrap things up?
Write the conclusion, summarizing the information. This should be the extent of the ending, as the conclusion of a cause and effect essay needs to be basic. Opinions, rhetorical questions and calls to action should not be included.
Reread the essay in its entirety to ensure that your conclusion adequately sums up the content. It should not be an extension of the previous effect section; it should stand on its own. Ask yourself if the ending answered to the content of the paper. For instance, is your conclusion a bit cursory or leave you with unanswered questions?