Assalamu alaikum.....I had found myself in the same jeopardy of how to start preparation.....after doing loads of research i came to the conclusion.......
1. you first have to decide your optional subjects......the best way to study a few past papers of the subject your interested in, obiously you can take professional advice too.
2.If it taking loads of time, then for the warm-up start preparing English precis and composition compulsory paper.
3. The second will help also help you when you read the Dawn newspaper. You will be able to make notes of the important points covered in the certain article.
4. Do not try to study for 10 hours from the start because you have to clear
CSS. try to increase your time slowly.
5. Last but not the least . Enjoy your reading and preparation because to clear your Css lots of extensive reading is required.
BEST OF LUCK.