Once you're familiar with the guidelines and limits for your assigments, you should engage in some "presearch." There will be things you don't know. Try to get a sense of your topic--get a solid understanding of the basics. Pay attention to the vocabulary that's used by others writing about the same topic. Try to get a sense of what others are saying so that you can confidently take an original approach.
Once you've settled on a general topic or area of interest, you can start to think about how to customize / personalize your paper within the context of the guidelines. Say you've decided to write about plastic bag pollution, ask yourself, "Who cares?"