Before reading the answer to this question, google the marks of a few UPSC toppers first. From the scores, we can draw the conclusion that marks in Essay and Ethics are either more or just beneath the optional.
How are Ethics & Essay scoring subjects?

1. The syllabus of Ethics and Essay is concise and the content for these papers can be taken from various sources. This can be newspapers, magazines and research papers etc. So, it requires less additional work while preparing for these exams.

2. Both Ethics and Essay papers demand crisp understanding of the surrounding issues. It does not require the aspirant to become a master in any particular topic. There is no fixed answer format.

For Ethics, your opinions on any particular matter should be clear and sorted. You can bluff out your answers in 3-4 questions but by the time the 14 questions are over, your character will be reflected to the examiner. Meanwhile, in the essay paper, try to make your essay as systematic and structured as you can. While linking the points between any two subjects the change should not be abrupt. The examiner here wants to feel the flow in your thinking process and argumentative capacity. Before writing the answer, it is advised to make a map of your thoughts.
Just by practicing the above mentioned points and choosing the right sources of material, aspirants can score good marks in these papers.
For practice of essay writing, you can refer to previous year papers or online sources like InsightsonIndia, AspireIAS, DrishtiIAS, EduRev to hone your essay writing skills. As a beginner you can take reference from EduRev, as it has 100 sample essays to help you understand the pattern of the essays. The app also has detailed and elaborated solutions to essays from previous year’s question papers.