my experience

My Strategy for Preparing General science and Ability

1: Before taking any book, take an overview of Syllabus
2: You will witness that plethora of topics are those which we have read in 5th class to 8th or Hardly 10th class.
3: Now, Books available in market edited by local publishing agencies contain copied data from various sources of Google which is just copied and paste stuff without knowing the fact that which thing is essential or not.
4: Next thing will surely e childish but is workable, collect science books from 5th to 8th class and match which topics in your syllabus are available in those books. Just prepare them from there. Most people will argue that it is CSS not 5th class exam but one thing they must keep in mind the Working of kidney will be same as in 5th class or in Graduation level. You will have to solve 5 marks or 10 marks question so, why you do not find an easy way to prepare. Moreover, Working of kidney or any other topic is explained more simply in lower classes books rather than higher classes so, it will be beneficial for those students to understand who do not have science Background.
5: Benefits: Your preparation time dramatically will shorten. Your syllabus for this subject will be complete in less time than usual. Use your saved time in Essay writing, Vocabulary building or any other thing.

Note: This is my personal opinion and it is workable for me.