Public Administration is a bit technical subject but not difficult. You can score good if you are well prepared, especially in context of current happenings with the bureaucracy. It means you will have to be abreast with current affairs, rather public administration current affairs, apart from studying good material.
For attempting Public administration paper do not forget to quote its theorists, experts and bureaucrats in support of your argument. This is the key to score high in this paper. Additionally, in each question you attempt show that you understand public administration as servant of public not the master.
There are some books available in the market. People suggest Dr. Sultan's books for Public Administration and Personnel Administration. However, I have never been satisfied with his books. Second option is Dr. Najia Younus. I haven't studied her book but heard about it being good. You may check this. Thirdly Virtual University Notes of public administration has been very effective.
The notes I am going to post below are made from Dr. Sutlan, Virtual University and some of my MBA notes. I hope they would help you in preparation.