This is a great initiative that you have taken and I think this exercise would help you improve your written expression immensely. Although I am not (yet) a qualifier of the CSS (My first attempt was in 2012 so waiting for result) and would not be in any position to comment on your writing but having worked as an editor and proof-reader of a couple of published books, I have tried to point out some of your mistakes. I think if you eliminate some of these minor mistakes your written expression would become more concise and also more precise. I have highlighted in red in the text below the areas which I think you can improve in.
Apart from the grammatical errors which I have pointed out, I think you can improve the content of your text by writing in more detail. E.g in the text below you have only stated why overpopulation is a problem, what are it's causes and what are it's remedies but you have not really analysed why overpopulation causes other problems like extremism, why is it caused by so and so like illiteracy and why these remedies that you have mentioned would work.
I think if you carry on doing this regularly and with the excellent feedback you are receiving by forum members such as Pearlys you will surely master concise writing concise English.
Date:July 29,2012
Overpopulation, Causes and Remedies
"The hungry world cannot be fed until and unless the growth of its resources and the growth of its population come into balance. Each man and woman—and each nation—must make decisions of conscience and policy in the face of this great problem."
Pakistan is facing a lot of the
(you can omit the here) diverse problem
(s) in the current scenario. Among the problems, one is overpopulation
(One of these problems is overpopulation *this might be a better way to say this as it avoids a connector and also a redundant comma*). It is ever-growing population that has been affecting the country in many spheres
(Ever-growing population has been affecting the country in many spheres *only a slight difference but it makes the sentence more precise*). In other words, it would not be false to say that it is the problem, which gives the birth to other grave problems, such as food crisis, terrorism, extremism, poverty, and other like in socio-economic and political spheres
(Overpopulation gives birth to other grave problems, such as food crisis, terrorism, extremism, poverty, and other socio-economic and political problems *again slight difference but you can easily make your sentence shorter and more precise by being direct instead using connectors etc*). Although, It is predicated that if in this way Pakistan does not prevent this alarming problem then in the 2050 the third most populated nation would have been Pakistan. So, It is crystal clear, that it is the alarming problem, which must has to be tackled in the priority option.
(It is predicted that Pakistan would be the third most populous nation by 2050 if population rates are not drastically reduced. Hence it is clear that this problem must be tackled with immediately. *When you write 'Although' then the next sentence or the second part of the same sentence must negate or resolve what you have said before so if you had written Although Pakistan would be the 3rd most populous nation by 2050 yet this could prove to be a blessing for Pakistan etc. Hence you cannot use 'although' over here. Anyway in my humble opinion you should strive to eliminate all these connectors like although, so, among etc. from your writing as these dont really add flow to the sentences and leads to confusing sentence structure. Also when you wrote 'it is predicted' it should always be followed by the prediction instead of other information for a logical sentence structure. Hence 'it is predicted that Pakistan would be....'*)
However
(No need for however here), there are a lot of diverse causes of this alarming problem. But
(Again no need for but and in any case I think you should avoid using but at the start of a sentence), the most causes are increasing rate of birth, decreasing rate of death, social influence, illiteracy, instability of government and government’s concurred departments which have been nearly failed to cope this problem such as in health sector, and population welfare family planing also the NGO’s inefficient role.
(I think a better way to wrote this whole paragraph would be 'The most important of the many diverse causes of overpopulation are: increasing rate of birth; decreasing rate of death; social influence; illiteracy; instability of government and government’s concurred departments, which have been nearly failed to cope this problem such as in health sector and population welfare family planing; and NGO’s inefficient role.' I know this a longer sentence than the one you made but I think it makes your point clearer in less words.)
As a matter of fact
(Again I personally feel you should avoid using these at all costs. You can start with 'Since the inception'), since the inception of Pakistan every possible strategy has been applying
(applied) to cope
(with) this problem, but owing
to the hurdles,
(no need for comma here) which are given above, this problem has not been solved like other western countries. However,
(I don't think a comma is needed here) for the solution of this problem,
(the) prevailing government has to work very
(I think very over here can be used but as a general rule 'very should be avoided as much as possible) effectively. The PPP government has little time to tackle this problem.
(This should not be a new sentence but a part of the previous one) But, with the Great Spirit
(with great spirit) it can be solved earlier. So, there are some steps,
(No need for comma here) which have to be taken by the apparent government in order to tackle this problem. Firstly, an effective policy has to be made and in this policy every possible action should be devised. Though
(No need for though here start with Priority), the
(No need for 'the') prority should be given to the
(again no need for 'the') education, family planing Tex connection and sex education should be given to the people in order to aware the masses of this alarming issue. Moreover
(This has been used perfectly 
), the concerned NGO’s have to be work for the same cause bilaterally.