For composition,
NEVER choose argumentative question unless ur english is very
strong. choose something like story telling one.
then when u write ur story, try to keep it as simple as possible.
keep ur sentences short. long sentences get mistake easily.
something like primary school standard will do. and most important
thing is ur grammer. and also, make sure ur handwriting is neat and
ur story is interesting so the marker can enjoy reading.
u may laugh at writing primary school standard compo but my friend
got an A1 for that. Argh... wtf sia
as for comprehension, i can't help u much. it is ur own
understanding of the passage. maybe someone out here can help u on
that.
anyway, all the best for ur O level. 