walaikum salam,
WOW, you have asked a broad question and it will be difficult to answer it entirely in detail but let me give it a shot :)
So, basically I think you should consider UK, USA, Canada and Germany. Apply everywhere for now and later on see where you get in.
It would help if you have seniors in your university or foreign educated professors who applied abroad and can give you a basic run down of the process.
For the USA you will have to take the GRE and TOEFL exams as well.
You should go to usnews.com, surf and look at the colleges of your field, go to their websites, go to the links for graduate admissions and surf around to see requirements and deadlines.
Make an excel spreadhsheet of all the colleges you are interested in [based on their ranking, location, cost etc] and their corresponding admission requirements and deadlines.
You could always surf to the Pakistani society or Islamic society pages of these unis and email people there if you have specific questions about the uni. Also ask them how you can get scholarships in that uni.
I am not too sure about the UK but I know that most graduate students in the USA get Teaching Assistantships and Research Assistantships but I have heard that these days because of the economic recession in the US, TA ships and RA ships are hard to come by. So, do some thorough research into it. You could also email Professors in the department of your interest in the unis you are considering and ask for their advice. Their emails are usually listed on the uni pages.
Hmmm...So now, the first thing I think you should do is start collecting information about the deadlines, talking to people, and preparing for your GRE.
hope this helps...
Best of luck and post back if you have more questions.