the best approach to prepare for CS as far as my experience is concerned, would be to sit in front of your computer having an internet connection, open google and search for notes of different subjects like database, networks, OOPS, programming, automata theory, data structure, computer architecture etc... it will come up with wonderful and easy to grab material with lot many notes, e_books, powerpoint slides etc.. scrutinize them and choose among them the best of best having the study material for the topics mentioned in the syllabus.. in this way you will have the required material to prepare for CS in your hands.. now all you have to do is to study them and build your concept..