Hello fellow amazing being,

This is my experience and approach. You can always disagree. No problem.

I had a very limited range of vocabulary. I am from Fine arts side and I had a long way to go.

For vocabulary, I did the following.
-I bought Barron's GRE book. Photostated the vocabulary lists and started cramming\rote learning them.
-I started reading extensively. I don't know whether the post "recommend me a book to read" is still here or not but I read some wonderful books that were recommended by the fellow forum members. Those helped me with vocabulary as well.
-I read news articles and if I didn't know any word, I would instantly google it and had a separate pad to write those words in. This is your formal writing training as well.

I found that CSS question papers usually ask words that are from GRE word lists.
It is not because they are looking at GRE word lists, nope. It is because those words are mostly university level vocabulary words that are often used in official correspondence and research papers; FPSC believes that we should all know these words.

If you don't have time to read books (we don't) or read articles (can't be philosophical and read long articles these days) then just memorise the lists. There is no other way. Cram them, rote learn them and revise, revise, revise.

About the lists:
I used Barron's lists. There are 3500 words in them.
100 words are the highest frequency words. That is their 100 words list.
Based on frequency, they also have next 500 words list or even 800 words list.
I saw 2,500 words lists as well.
However, again please know that you can't be sure these words would definitely appear in the exam but doing these lists would increase your chances of gaining 10+ marks in the objective paper.

Kaplan offers word lists for GRE as well so do several other websites. No harm in doing those words as well.

I found some websites to help you.

1-Vocabulary.com (Has a Barron's 3500 words list. Make an account and start going through those in a multiple choice format.)

2- Quizlet flash cards

3-Cram flash cards

4- Pdf for you to print out.

Knowing Suffixes, Prefixes and root words are good but English is a tricky langauge and often meanings change even with similar suffixes or whatever. I just had to time to deal with the whimsical nature of the words so I didn't spend time on that.
That's about it. Thank you.