I answered factual essay last year and i scored A1 in GCE-O.
The question was Examination, Good or Bad?
I was very very lucky because I just did that essay 3 days ago, which has similar title "the advantages of examination".

What you need to score factual essays:
-Impressive and correct facts
-Coherent language use
-Wide range of vocabularies, with relevant usage of words
-Clear stand (either you agree/disagree or stand on the fence)
-KNOW RECENT NEWS or related news
-Organized paragraphs

that's all i know... And remember to read a lot. I am trained to do factual essays, so i can't write narrative/descriptive at all. I ALWAYS do factual, and it never failed me~

And who said factual not advisable to do? It's easy to score if you are on the right track...