The first thing to do with commerce is to get your hands on a good book. The one in blue by Betsy Lee is very good. Secondly, for your paper 2 make sure that you go through all the qsts before selecting the one's you would do. This is to make sure that you read every part of the qst and are satisfied with it.
Next, be precise in your wording with the 1,2 mark questions. Don't write vague sentences. For the next parts be very sure that you are answering "in the context" of the question which is the situation that is given in the questions. Trust me if you're not doing that you may end up in a B! Its one of their major assessment objectives to test context. For the last question, don't write introductions. Start with your reasoning. 4 solid points, well explained would be ample. And lastly write a concluding paragraph. You should show clear judgment in that of what you have written above.
....Go at all questions like this and you soon make up for an A*.
For the mcq's don't bother much about the textbook. Do past papers 2002-2009, would be adequate. Understand the question, do not just learn the answer.