When teachers allow you cheat sheets for math tests, in addition to writing down formulas, I recommend writing out examples of problems you don't easily remember the steps to. Whatever you think you'll have trouble recalling during the test, write it down. Sometimes the examples you write down are very similar to questions on the test, which will significantly help you recreate the answers. Also, study your cheat sheet. Do not fill it out and then not review it. If you don't know where to find the information you wrote (quickly during the test), then it's useless to you. Know your sheet!
When taking math tests, there are always lots of equations to remember. Some teachers allow cheat sheets on which you can write down various formulas and example problems. Others don't, and you have to rely on memorization. When this is the case, I recommend the following - First, memorize the equations during your study time by writing them out on scratch paper several times. Repeating them helps them sink in. Second, when you get the test, the first thing you should do is write down the equations/formulas on the top of your paper before you start solving problems. That way, you won't twist them around as you work other problems, or forget them during the test due to normal test anxiety.