My one piece of advice - which needs to be put into practice straightaway so you have time to get used to it before the exam period - can be summed up in the two simple words: For example
What do I mean by this?
Nearly all students, not just those who find English a chore, are inclined to express their first reactions to an exam question in general terms. This is a natural reaction and serves as a release.
Suppose the task is to write as follows (the question is taken from a recent GCSE paper) :
A friend or a relative has decided to become a teacher.
Write a letter to him/her giving your opinions about this decision.
An answer in general terms could possibly say something on the lines of:
'I think you have made a good decision. Teachers are very valuable members of society. Helping students to learn is very rewarding. Teachers do not earn as much money as in some other professions but they have job satisfaction. They also have long holidays etc.
Fairly soon the broad opinions will dry up. And then what? You don't want to start repeating yourself because examiners are always looking out for that.
This is why the For example strategy is so helpful. A sentence beginning For example can be launched after most sentences of the above - and then, with a little thought and practice, the dull essay task can be transformed into entertaining and effective writing.
Let's go back to the general draft.
Teachers are very valuable members of society. For example ... I think of Miss Jones, when I was at Primary School, who played the piano and taught us songs for St Andrew's Day. Without her I might never have joined the choir and made singing my hobby. I know you that you are more of a sportsman than a musician, but wouldn't it be great to coach the basketball team and maybe bring fame and success to the school?
And so on. Out of one unexciting generality, the For example can lead to a world of possibility. It doesn't matter if it is true, or made-up or a mixture of truth and make-believe. It just has to be realistic. And if the English is not flawless, the originality of the example stories will count for far more.
Do give this advice a go. But don't leave it until you are in the exam hall. Every little art requires practice. For example ...