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.
(Real advice: 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.)