"Describe a person who has had an impact on your life, positive or negative. What influence did this person have on you, and how did you learn or grow from that influence?"
An important part of answering this question should always be to pick someone who has had a positive influence. Although the question may state that you can use negative experiences, try to avoid going this route. Show the college admissions board that you are a positive person by picking a positive experience, even if your life while growing up was less than ideal.
"Describe what profession you plan to pursue. Explain why you chose it, and what you hope to accomplish by pursuing it."
Here is where you should show excitement and passion for your chosen career. Avoid saying things like "I hope to become a businessman so that I can make lots of money." Show the admission board that part of your working life will be spent helping others. Try something like "I hope to run a business that will enrich the community through fair trade practices."
"Describe a problem in your personal or academic life. Explain how you solved it and what you learned from it."
Colleges are looking for adult-minded individuals -- those who don't blame others for their problems, and who take full responsibility for solving them. Make sure that your answer reflects these attributes. If you learned how to avoid the problem in the future, that should also be part of your answer.
"If admitted to our college (or university) what do you plan to contribute? How would you make the campus or institution a better place?"
Research the college before answering this question. See what problems it has had in the past (such as lack of funding or qualified teaching assistants) and correlate your answer to those issues. This will show the admissions board that you are truly interested in helping the college in areas where it may be lacking.