Hello!! Ill suggest you that ,you better to prepare yourself,because WBCS examination questions will be at graduate level,it isn't that difficult to clear the exam.Better to go through NCERT and state text books before going for other one.You just go through the examination syllabus and make plan for preparation.After preparation take an online assignment to get confidence on the topic covered.And..this is what the online coaching centres do giving you study materials and online assignments .So..that you can do by yourself.

https://competition.careers360.com/articles/wbcs-syllabus

https://competition.careers360.com/articles/wbcs-exam-pattern

You just go through the above links ,which consists of syllabus and exam pattern.Prepare well with concentration.All the best for your Exams!!