a tip to do well in maths is to not get cocky and think that you will do well, because you always end up getting disaapointed. my maths teacher said to skip problems if you dont know how to do them, or just guess it. If its only worth one mark, guess it, and go on. remember to not place two answers in your test, because now they count it as wrong (i used to put three multiple answers and they accepted them, but not anymore). ALSO, make sure that if it doesnt say to round off, then dont! keep it in the long way or as a fraction, because I GOT ONE MARK TAKEN OFF FOR ROUNDING IT OFF!!! STUPID TEACHER!!!!
if you dont want to make stupid mistakes, then try to check your paper in the end. What tends to work is to turn your paper upside down or cover your answer, and do the question again and you will find whether you made a silly mistake. people make stupid mistakes because they assume it is right, since they know all the stuff already. its the same with english. usually, people cannot spot errors in their work because they wrote it themselves and know what its supposed to be read as.
DONT LOSE YOUR CONCENTRATION IN ANY EXAM. ohhh and i find that when i encounter a hard question, i lose all belief in myself. I advise to treat every question individually and to not be put down by one hard question. If you cant finish the whole paper because you dont know how to do the remaining questions, then dont bother with trying how to work out how to do the remaining problems. Go back and check the problems you have already did. At least you can make sure you have those marks secured. It would be pretty sad to have marks taken off for questions you havent done and also marks taken off for silly mistakes in questions YOU CAN DO!!!