Apply early: courses can fill up quickly, so make sure you apply early. A Master's degree is more specific than a Bachelor's degree -- providing you with the opportunity to select a course that is aligned with your interests. Select something that shows an employer you're passionate about working in a certain area. Early applicants also stand a better chance of being awarded a bursary or scholarship.
Location: deciding where to study is a huge decision that will affect your lifestyle once you're enrolled in a course. Make sure you choose somewhere you'll be comfortable and happy to spend time. Think about how far you wan't to be from your home town, and how expensive it will be to travel back if you need to.
Experience: to get the most out of your course, it's beneficial to have experienced what you're about to learn in a practical environment -- achieved through an internship or work experience. For political science students, it would be good to gain experience in a political organization or at a government department; whereas for finance students, some time in a bank or accountant firm is recommended.
Reading: It's also worth doing some pre-reading before the course starts. Suggested materials are often available online, and by being pro-active, you can help your professors remember your name.
Money: wherever you choose to study your Master's degree, it's going to cost a lot of money when you factor in accommodation and living expenses. Make sure you have enough to keep you going throughout the year -- you don't want to have pick up the phone and ask friends or family to unexpectedly help you out, or even worse, have to take on high interest credit.
Job: depending on the amount of classes you have, you may want to get a job to help fund your course and provide some extra dollars for enjoying yourself. Competition for jobs in student towns and areas close to schools is high, so it's worth going online and having a look for bar jobs or temporary work before the course starts. Pick up the phone and explain your situation rather than sending prospective CVs.
Living arrangements: accommodation can be expensive, particularly if you're forced to use non-university accommodation and rent privately. You should know your expected living standards by the time you're working for a Master's, so think about these requirements before committing.