Don't use conjunctions, "it's" and "you're" become "it is" and "you are". Helps with word counts, and makes your essay read more formally. Either properly set up a transition when you're ending a paragraph and writing a new one, or if it's your conclusion, make sure the last sentence has an air of finality and it ends on a high note, so it can properly recognized as the ending, and not just another bit of information. If you're looking to make the essay look longer than it really is, larger font, a different font that takes up more space, or make it double-spaced, if any of that is allowed. However, usually if you properly research your topic, you'll have more than enough to talk about.