Having the right ski clothing is as important as having the right ski equipment. If you aren't dressed properly, it could ruin your whole day. If you're cold or get wet, you won't have fun. If you have too much bulk, you won't be able to move well. Follow these simple guidelines for purchasing the correct ski apparel and you'll be stoked on the powpow.
The first layer is the layer closest to your skin, and really is the most important layer in a ski outfit (often called "long underwear"). If you wear something that doesn't have any wicking ability, meaning it gets wet and stays wet, then you'll get wet from sweating (or maybe from snow getting down your pants from a fall), and stay wet all day. If your first layer is wet, that means you'll be really cold, and you do not want to be cold. When shopping for a First Layer (this is the term used in ski and sports shops), stay away from anything that is 100% cotton. You want the new fabrics that keep you dry and warm, some are made of wool (if wool makes you itchy, read fabric contents carefully), some are cotton blends. With modern fabric technology, there's no reason to be cold. Smartwool makes a great first layer, as does the snowboard company Burton.
The second layer is the pullover, or fleece. You won't want to wear your first layer, only, and then a jacket. You need a second layer over the first layer shirt, and this can be a fleece jacket or a zip up made of the new fabrications, or something that partially zips and covers the throat (a short turtleneck with a zipper). Companies that make great second layers are Patagonia and Oakley.
Buying pants and a jacket are a matter of taste. You can buy something that matches, and are from the same company, or you can mix it up. Skiwear can be expensive, so look online for sales at sites like backcountry.com. Every company has a different fit - what's a Large for Holden can be a Medium for Oakley, so when buying online, know what fits you best and is the most comfortable. Make sure you can bend your knees with ease, and with no pulling in the crotch. Be sure you can hug yourself with ease, and that the shoulders aren't tight. You need to be able to really move in these clothes. If you like extra warmth, some pants come with a fleece lining, but remember that skiing does make you warm, you are working hard! Skiwear has waterproof and breathability ratings and are important to note: if you're skiing the East Coast, look for a minimum 10,000mm. If you're a spring skier, then 5,000mm is perfect.
Another important item to purchase is socks. Do not wear any sock, wear a ski sock. Again, wicking fabric is key, here, you don't want wet feet or you'll get numb and not be able to ski. A ski-specific pair of gloves and a helmet finish your outfit, be sure both fit well.