Choosing a topic to write about can be tricky.  You should always keep three things in mind:

1) Previous Knowledge-- Is this a topic you already know something about? It is acceptable if the answer is "no," but in that case, you will need to do more basic searching to understand your topic fully.

2) Course Content-- Does this topic reflect an idea that you are learning about in the course you're writing for?  If it doesn't directly relate, is there an angle you could take that would? 

3) Personal experience or interest-- Is this a topic that will keep your interest long enough for you to write an effective paper about it?  If you're not interested in writing it, it won't be that interesting to read.

Also, remember to think about multiple facets and angles for your topic.  If your paper is meant to be argumentative- is there an argument to prove here?  In other words, are there two or more sides to the issue?