The people reading your essays are regular human beings, which means you should write with that in mind. A good way to check your tone is to read your essays out loud. No, not in your head, out loud. Read them to a friend, parent, sibling, whatever, and if you feel embarrassed or uncomfortable by the style, then you should change it. This doesn’t mean you should add in colloquial filler words like like, um, and uh, but it means that the essay should flow smoothly enough that you feel comfortable reading it out loud in front of someone you don’t know very well (don’t actually do that, but you should feel good enough to).