Academic writing, unlike creative writing, generally follows a set formula, allowing for a clear structure to an essay to act as the backdrop to your argument(s). Often, your course guidelines or essay title will define this structure but it will generally involve an introduction, some background to the main arguments, perhaps through a literature review, some analysis and then a conclusion. Although all of these elements are important in their own right, many would consider that a good conclusion is the mark of a good essay. The reason for this is that all of the earlier elements such as the introduction, hypothesis and analysis, are all reiterated within the conclusion, making the conclusion the summary of all of your research, theorising and review.
Once you have written your conclusion then you should check your entire essay for spelling and grammar mistakes, and that you have followed the required style and referencing guidelines throughout. And most importantly double-check that your conclusion really does conclude something!