Pay attention to the number of marks per question, and answer accordingly. A two mark question only needs one or two sentences (maths is obviously different). A six mark question usually requires about 1/2 - 3/4 of a page. And don't let the number of lines they give you mess with your head. The marks are more important than the lines. The last question in our year 11 music half yearly had heaps of space for writing, we all went nuts, and wrote like, 2 or 3 pages, and then realised that it was only a 4 mark question.
If you get stuck, then make a note of it, and come back to it. You're better off leaving a question half answered and getting through everything else, than fully answering one question, and leaving another 3 or 4 completely blank because you ran out of time, because they can't mark what you haven't written down.
Make sure you use your reading time. When you go through, look at questions where you have a choice of more than one thing, and work out which option you'll take. Look at the marks allocated for each question. When you've gone right through the paper, use the rest of the reading time to do multiple choice questions, read comprehension texts, plan essays etc.
