I would recommend you to visit PACE CSS Academy G-10 Markaz Islamabad near Babri Masjid. They train all of their students and assess them individually(on daily basis) unlike other academies that only deliver lectures and ask the students to go and read the notes. There is a free CSS exam training sessions on Sunday, 13 of October (morning, afternoon and evening). You can visit and ask any question from the trainers. Best of luck!!