Yeah, I was very confused back when I was writing my essays as well.
You should, of course, be yourself and be honest; don’t make things up. However, when sources say “Don’t try too hard to look different,” what they may be referring to is being too honest in order to stand out. If you write about something that is overly abstract, scandalous, or controversial, you’ll look different, but in a bad way. I always think of this article: http://www.nytimes.com/2014/06/15/opinion/sunday/frank-bruni-oversharing-in-admissions-essays.html?_r=0.
But you should make yourself stand out. The best way to do this is to think about what defines you: What is your best quality? What is your passion? What is an important lesson that you’ve learned that you try to live out daily? This can be something that not many people have done, or it can be something mundane; it all depends on how you write the essay. When you write about something truly important to you, you’ll find that it was influenced by many factors such as your race/ethnicity, beliefs, past experiences, and relationships. There may be many people who have had the same isolated experiences as you, but no one’s done them for the exact same reasons and in the exact same ways as you.
Also, you don’t have to avoid overused topics, necessarily. Maybe you volunteer at a food pantry. You could write about that. Or you could write about how the food pantry is an hour away, and you have to take the bus to get there once a week. And at first, you thought, “Why am I giving up so much time to help people load carts of food, when I could be doing something closer to home?” But then you realize that you live in a pretty affluent neighborhood, where there is a huge stigma against the poor. This food pantry is your only chance to get out of your little bubble, do something about the issues in the city you now consider part of your community, and learn humility through service. Putting a spin on a cliched topic will help you come across as mature, introspective, and creative. But it’s hard to pull off. So if you don’t have that much introspection about why you do the things you do–I know I didn’t at that age-- just choose a less common topic.