Make silly computational errors at the start of your work, so you end up solving entirely the wrong problem.
Effect: Much like in real life, the best way to do something wrong is to do it wrong from the start.
(Real advice: BE CAREFUL at the beginning.)
Give wrong answers that you could have easily verified, like the solutions to equations.
Effect: You will come across like you don't actually understand or care what the solution was for.
(Real advice: CHECK YOUR SOLUTIONS by plugging them into the original equations.)
Write down random formluas from the course, and randomly set expressions equal to 0 or each other.
Effect: The grader will think you don't really understand what's going on.
NEATLY SCRATCH OUT your irrelevant work at the end. Experimenting can help you remember
or discover something, but don't expect someone to read it.)
Write all your workings in a random order, with no explanations.
Effect: The grader will have no idea what you're doing. This will also help frustrate the grader so he/she has to spend more time grading.
(Real advice: ORGANIZE your work, and use SHORT SENTENCES to explain what you do.)
Don't write any "=" signs.
Effect: This is similar to writing an essay without verbs. You can't be right if you don't make any statements!
(Real advice: USE "=" SIGNS where appropriate.)
Misread or mis-copy the problem.
Effect: Something like installing an air conditioner in the arctic.
(Real advice: READ CAREFULLY what the problem is asking.)
Leave the exam early.
Effect: Wow, you're the cool kid who leaves early from the exam everyone else rocked because they checked it over.
(Real advice: If you finish early, DO THE EXAM AGAIN. Have the courage to sit in front of a math exam for the trivial amount of time left on the scale of the semester.)