Remember to seek out sources that disagree with your perspective on a topic (if you go into your project with one) instead of just looking for sources that agree with you!
Why?
Your perspective may change, which is not a bad thing. It shows you're open-minded enough to respond to research that disagrees with your initial perspective.
Counterarguments address the other side of the issue, and they make a paper stronger. By engaging by those who disagree with your perspective, you cut them off at the pass---that is, you respond to their arguments before they can make them. For example, if my paper argues that the myth and culture surrounding the idea of mermaids matters more than whether or not they exist, someone on the other side of the fence may argue that, because myths are rooted in fact, determining the facts make the myth stronger. My response may acknowledge that this idea has merit, but a myth still exists whether or not it is based in reality.
Including counterarguments adds new depth to a paper and allows you to demonstrate your critical thinking skills in a sophisticated way.