Dude academy is time wastage and money wastage. They only teach properly for first 15 days or so, provided they can arrange teachers for your optional subjects. I joined an academy, paid dues in full and left after a month and a half for this reason.
As far as your question goes, as you are commerce graduate, do opt for accountancy and auditing, mercantile law and either business ad or public ad in your optionals. This will give you a major edge. Use your own previous notes for these subjects. For others go to urdu bazar to get some good books, consult net and if possible buy some good notes from academies. Go for focused studies on your own. That means at least 5-6 hours daily in initial months and about 10 hours in last 3-4 months and with help from Allah SWT you stand a fair chance of passing CSS in your first attempt. Also, make sure you know your strengths and weaknesses so that you can allot more of your precious time in overcoming your weaknesses. Best of Luck!