There is a lot of confusion about giving a sketch and headings in an essay..
my findings are.... giving sketch at the start of an essay is one of the good practice.
I recomend that a sketch before the essay gives your reader the idea of what you have given in the essay. It makes his work easy and the more you make for the examiner his work easy the more you will get marks.

As far as headings are concerned ..they were previously no appreciated and were considered negative. Though the trend has changed and a few headings are not discouraged nowadays. Still you don't know about the one who checks and as it is against the basic rules of essay to give headings so can be a negative point. It is better not to give headings and underline the part of the sentence in your para which should make your reader understand what is about the para. This is enough toi make his work easy.
(Yahya Akhunzada,DMG Officer)

Length of the essay (Miss Mediha,FSP)
ASA,
Since i took my O'levels, we were trained to think out and outline our essay before writing.. i think that is indeed a very healthy way of writing, and it makes the essay coherent, flowing and well connected and very readable.

Also, another point on the essay that i would like to give out is that please, dont write a 'run of the mill' essay and go on for pages and pages and pages with empty rhetoric.. that is NOT what is required.

I wrote my essay on 'On tolerance' and believe me, my essay was philosophical, factual and opinionated on what i felt. AND, it wasn't for 20 pages.. I think it went the length of about 15 pages MAX..
think out the essay well, be careful in chosing a topic and write from the heart (but nothing that makes u sound like a rebel without a cause)