Be very careful in guessing.
Try not to guess as far as possible.Guessing should be the last last last resort. A few tips from my personal experience, if at all you have to guess.
1. No matter which part of the test you are, never guess questions in a row. For example, if you're stuck with a very difficult RC passage, DO NOT arbitrarily guess all the questions. I honestly believe that doing that reduces your score by quite an amount.
2. Never guess more than 2 questions in a row towards the end. My experience makes me believe that these questions count more than the questions in the middle of that section.
3. Even while guessing, try to narrow down to "sane" choices so that you increase the possibility of getting the answer correct.
Last but not the least, be very careful of any last minute advice from friends or anyone else about guessing. Guessing,IMO, should be the very last resort,and try not to use it as far as possible.
Do not change your strategy(or, as some would say,the winning mantra) a couple of evenings before the exam.
Cheers!
StellarRose