One piece of advice:
Look at your answer and stop for a moment to reflect on "Is my answer REASONABLE?"
Not "Is my answer CORRECT", as that is often a difficult question to answer, but is it reasonable... a lot of silly mistakes can be caught by recognising that an answer is not reasonable.
For example, find the third side of a triangle given the other two sides and an angle. Using the cosine rule, if you have sides of 5 and 9 and find the third side is 52, that is UNreasonable. The answer must be between 4 and 14 or you can't get a triangle. The likely mistake is having answered with
rather than
(i.e. forgetting the square in the cosine rule and so not square rooting to get the answer). As a tutor and a marker, I can say with certainty that many mistakes are made that lead to obviously unreasonable / impossible, or sometimes even just very implausible, answers... and this is true in the sciences as well as in Maths.