MCQs are not hard nut to crack if one has gone through the basis of scientific concepts. Start from the basic science book like that of 8th class. O/A levels science book is also good source. When you read most of the scientific topics you will get conceptual understanding of the topics which will help you alot in MCQs.. After doing all this you may come to Kashmiri and other CSS related books.. You will notice the improvement and feel comfortable while reading CSS related books. The second good source is Internet...
HowStuffWorks - Learn How Everything Works! is an excellent website where you can get your concepts cleared. There are many MCQs books available in the market. Candidates try to cram these MCQs, it may be beneficial to some extent but most of the times it does not help. These MCQs book can also be handy if you know basic scientific concepts...Many MCQs get repeated in CSS again and again so solving past CSS papers help alot. I myself solved lass ten years CSS papers and scored 75 in this subject.