Well. It is good to hear that you want to improve your English for the會考, I bet your school did ask you to do a lot of practical grammer exercises, which sure helps your grammer. But if you needed more ideas in writing part, you maybe try to read some interesting articles in the English magazines. Do not try to read South China Morning Post because it is really boring, you will lost interest easily as you have to look up dictionary a lot. Or even borrow some simple story bookd from library, it sure helps a lot too. Good luck
其實如果講英文文法,一般你學校用既教科書都已經幫到你。反而,與其盲目甘浪費金錢,我會建議你每日嘥幾蚊買份South China Morning Post, 揀D你有興趣既新聞黎睇。唔需要花太多時閒,可能只係利用每日搭車,去廁所既時間,一黎可以真正明白英文句式既用法,二黎又可以豐富自己既知識,對英文作文好有幫助。而且,報紙裏面所用既字眼,都係一D最正統,最恰當既。