Personally, I wouldn't talk about leadership skills in my PS because it is too cliched anyway and will not make you stand out. Have you actually gained any skills from being a Uniform Monitor? Is it really relevant? If you are eager to include it anyway, make sure you relate it back to your subject, e.g. if you're applying for law, say how it helped you learn to pay attention to detail, be persuasive and resilient, etc. (any qualities that lawyers generally possess). As a general advise, make sure everything in your PS relates back to your course.