I’d suggest you start with a proper pre-work. Before writing your essay, read the original text thoroughly. You should grasp a good understanding of the author’s style, tone, mood. Also, it is crucial to gain a good understanding of author’s ideas at this very point.
Next thing you are advised to do is to divide the text into sections and create an outline. This would serve as a basis for your future essay. In this simple way, you will also ease yourself the process of grasping the material. Highlight the key points, mark ideas and areas which you plan to put into your essay.
Once you’ve done all that, you’ll get the clear understanding of the source. It is the perfect point to start writing an introduction. It should briefly present the main ideas in the original text and include the name of the author, the title and background info about the author (if needed).
You can follow the basic structure, to make writing easier.
Do not include your own opinion about the text at this point of your writing. Good luck!