Read More to Write Better. When we read, we learn more. For writing the best & relevant answers it is very important that you keep reading more and more.
Write to the Point. Don't write hefty answers. It is the myth that long answers score more marks than short ones. It is not at all about long or short answers. It all depends on the relevant point
Prepare A Writing Structure. You can't just start writing the answers without knowing what points should be covered. The most general structure is to write introduction then write the points/paragraph required.
Don't Be Too Generalized. Remember you are writing an answer and not a novel. Don't be too philosophical or generalized while writing the answers.
Improve Basics Like Tenses, Grammar, Etc. Whether you are attempting UPSC exams in Hindi or English, Grammar is very important.