Brainstorming and Prewriting
Start with brainstorming your topic. If you work well with lists, write the word at the top of the paper and fill the rest of the page with all the things that the word makes you think of, feel, see, or even smell, without stopping. It's OK to go off on tangents, as you might find a surprising connection that could make a powerful, insightful, or even humorous essay. Alternatively, brainstorm by writing the word in the middle of your paper and connect other related words to it and each other.
As you develop your angle, think about the concept's background, features, characteristics, and parts. What is the concept's opposite? What are its effects on you or others? Something in your list or word map will spark a writing idea or theme to use to illustrate the abstract concept, and then it's off to the races. If you run into a dead end the first time, go back to your list and pick another idea. It's possible that your first draft turns out to be prewriting and leads to a better idea that can be developed further and can possibly even incorporate the prewriting exercise. Time spent writing is time spent exploring and is never wasted, as sometimes it takes a bit of pursuit to discover the perfect idea.