firstly, you have to understand that you CAN actually avoid silly mistakes. some people just accept that they can and will happen, but that is not entirely true, as you can prevent them. My advice would be to go slower than you usually would, and in particular to take extreme care with questions on which silly mistakes are easy to make (angle between two lines, internal and external ratios, pretty much anything that involves substituting numbers into formulas). with checking over your work, some people like to redo the paper, but personally i dont think this is great. when youre checking your work, just try to go from step to step and see how you actually got from one line to the next, rather than just skimming through. it'll take longer but it will be worth it.