In my view essay writing in CSS exam requires;
1) outlines,
2) knowledge alongwith references,
3) simple english means less spelling mistakes mistakes,
4) less grammatical mistakes.
In this condition u can get through essay paper. (45 -55 marks)
If u feel that u r not confident in writing essay on CSS level due to English, simply take an urdu essay on given topic and try to translate it yourself.
Remember to be simple but having much points means knowledge/information and references in essay writing.