I agree with Simone -- there is no reason you can't argue one side of the issue very strongly, if you are permitted to do so. Generally, it is a good idea to raise some of the main objections to your argument, so that you can demolish them, if you hope to be truly persuasive. Of course, for the test, you may only care about creating a solid essay in a short amount of time, in which case, raising the opposing point of view is unnecessary.
If you really want to remain neutral, though, either because you have to or because you have decided you want to, then the idea would be to present argument, counter-argument, counter-counter-argument, and so on, until you reach the point where people have to agree to disagree because the issue has been reduced to a matter of principle or of personal preference. Put another way, you would start by presenting both sides of the issue, then break each one down until you found the point where their premises diverged.
Sean, EssayForum.com