Anyone who has to take the GMAT knows that the test can be difficult and hard on the nerves. It doesn't have to be like that, though, if you're well-prepared for it. There are free options, friends who can help you study, and books you can buy, but to really be prepared you need to take a good GMAT course. That way you'll be as ready as possible. You'll understand the format of the questions, you'll know how to deduce answers that you aren't sure about, and you'll have a lot less anxiety. Because every question has an answer, the one you should be asking yourself is how to get the best GMAT prep that you can find.
Look at some of the options out there. See what the cost is, what they have to offer, and how they work. Not everyone learns in the same way, so you'll want to address your particular style of learning in order to get the course that's right for you. Take your course in plenty of time, too. You don't want to be cramming information at the last minute, because most of that won't stay with you. Rather than leave everything until the last few weeks, start studying early.
When you study for a longer period of time, you have more of a chance to develop critical thinking skills. Those will help you answer questions more accurately, and also help you figure out where your weak areas are, so that you can spend more time on them. That way you'll be as prepared as possible, so you'll be less stressed on the day of the test. Stress can stop you from performing to the best of your abilities, so it's something that you'll want to avoid if possible. Being ready for the test is the best way to alleviate most of your stress.