kindly guide me what key points must be under consideration while devising an outline of an Essay? which general issues must be kept in mind regarding to essay topic...?

First go to the past papers and collect some good outlines written by candidates in essay papers. Then practice them. find out good and bad aspects of those outlines.

try to practice on standard pattern such as
Introduction
Current Scenario
Effects
Causes
Solution
Conclusion

For example if you are talking about effects of energy crisis write
Squeezed Business Activity
Eroded Confidence of Domestic and Foreign Investors
Stagnant Tax Revenues

You must use good adjectives to highlight the aspects. Make apt use of Colon, Hyphen etc.

In my own view long sentences should not be written in outlines such as " energy crises contracts business activity"

If you are presenting argument such about computer bane or blessing, your outline must cover favoring and counter arguments.

Not only for essay but also for current affairs and pakistan affairs and other subjects you should practice outline so you can quickly organize your answer during the paper and that you may not get confused in organization.

1. Brother can we site history of relevant topic in an outline?

2. As in current affairs and Pakistan affairs it is strictly advised to be relevant to the asked question. But in case of essay can we give a comparison? i.e suppose we are asked to write an essay on "Good Governance in Pakistan", can we compare it with good governance in developed countries?

3. As you said that "If you are presenting argument such about computer bane or blessing, your outline must cover favoring and counter arguments." in this case are we not asked to choose one stance, either to support ban or to support it as blessing?

1. Actually there is no pet rule... some people Discuss history with separated outline like history of good governance in pakistan.. but in my view it is very old style of writing.. i use to discuss history within my essay such as while discussing causes, effects and solutions.

2. About good governance in pakistan your focus should be pakistan, in my view don't give separate outline such that comparison of good governance with other countries but discuss such comparison while discussing causes of bad governance, effects of bad governance steps needed to promote good governance. ( this is my view not pet rule).

3. Off course you should focus and argue your side like if you favour computer as blessing then keep your whole essay revolving around this point of view but dont forget to discuss counter arguments because computer has many negative sides also. NO statement is universally true.