Read and re-read the textbook, solve past papers and do not forget to check the marking schemes-if a question is re-assessed on, u must write the answer almost exactly as its answer was given in the marking scheme by putting it in the context of the question. Just think what else u could do to make urself feel prepared and revise the specification areas u appear to be weak in. And yes, do not simply keep the book in front of u. If u r tired, have a rest. Get started when u feel fresh and active but make sure u do not waste ur time in just sleeping. I know simply reading the book is not enough. Why not try some active approaches?