The first key element to writing a good essay, is to make sure that you cover every topic that could help improve your essay. For example, if you said: "Humans have evolved as a species."  You would have to give an example, Like:"Humans have evolved as a species, because they can communicate and collaborate better." This makes a point and shows evidence for it. If you wanted to make the essay even better, you could write another sentence about how humans communicate and collaborate better, and what they have achieved by doing that.