Dear Friend...
As far as essay, Current affairs and pakistan affairs (Current Portion)are concerned... the best source is Daily DAWN.....

Further I will sugest two digests...

1. Strategic Studies Digest (issued quarterly by strategic stufdies department Islamabad).... get atleast it coppies of current year...
2. National Development and security (issued quarterly by Friends Association Rawalpindi) get its one year coppies atleast.
These two digest will help u understand the style of essays.... though its topics are given in headings but in essay it is better u do not go for headings but devide ur essays in different paragraphs....

Similarly if u want to know the backgrounds of some topics then go for Imtiaz Shahid's Current affairs digests.... (as time is short so u do not need these digest to read in detail) if u can get them just read only those things which seems and are important according to ur choice... The disadvantage of this digest is that its english is toooooo tough and difficult... I had not consulted this digest ever....

Now how to prepare

1. The first thing u need to do is find out the important topics related to Pakistan, USA, Pakistan's neighbours (India, China, Afghanistan, Iran, Central Asian Republics) Russia, N/korea, Iraq, Muslim world inn general etc....

Let me give u examples
Pakistan..... the topics can be listed as following

1. Kashmir

2. Relations with India, Iran, China, USA, Afghanistan.... any new happenings and all that has been done in this year.

3. Pak India relations in the light of trade, kashmir, water etc...

4. LFO controversy (views of govt, MMA and ARD), Presidents uniform, Elections and its after maths

5. Democracy its future.... role of MMA, government views, effects of LFO, Uiform president, Army role, politicians, bureaucracy, NSC etc....

6. Economy in detail including the macro econmic developments... its effects... no interest in social indicators and its effects, debt trap, FDI .... (economy should be done in every aspect)

7. Poverty Alliviation

8. Water dispute.... Construction of Dams and canals.... views of different provinces, need, objections.... complete picture of the problem.....

9. Role in Iraq, Palestine, Afghanistan... War on terrorism etc..

10. Role in OIC, UNO, SAARC etc

11. Reforms of previous government specially economic and in education

12. Education
USA...
1. Usa world Policy
2. USA policy towards Islamic countries
3. USA and the net election year
4. USA and North Korea
5. USA and War on terrorism
6. USA And Iran
7. USA and UNO, NATO, EU
8. USA role in IRAQ and Afghanistan
9. USA and WMDs
etc...

North Korea.... Nuclear Crises

Palestine.... Peace initiatives... role of USA and Muslim world

Central assian Republics and its resources a source of world convergence or conflict

just chk all the current important issues and find related meterial from the editorials, world in focus and magazines of the dawn and other available meterial....

Now imagine the kind of essays that can come on these topics...
Next step is to make the outlines of these topics and revise in ur mind how u will manage ur essay....

Now from the meterial get some impressive starts and conclusions...
If possible write 2 or 3 good essays on the most wide and important topics like
1. changing world scenirio..... US and Pakistan role
2. Economy of Pakistan
3. Democracy in Pakistan.....
These essays should be from the meterial u have with an impressive start and impressive conclusion....

This will help u automatically in preparing curretn affaairs and pakistan affairs (current portion)