Essay writing is an apt way of judging the students' command and grasp of a language and of its grammar, be it English or German or any other language for that matter. 9788183073578
The key to good essay-writing is constant practice and a lot of reading, which is also a great help in improving one's vocabulary.
To sum it up, it is by and large self study.
An interest in the language is but a necessity, and also the first step in familiarization with the language

German Essays for Class X CBSE Board