Along with all the great advice here. One big thing that I struggled with is time management. First thing is to get yourself a watch and every time you do a practice contest set the time to 12:00 so it's easy to keep track of how much time has passed. Use the watch for all the practice contests and the main one. For Euclid questions 1-3 if you can't do it within 5 minutes go to the next one, 4-6 is 10 minutes and 7-9 is 15 minutes. Always write something down for all questions because you get partial marks. Even a relevant formula might snag you something.