1) Skier's weight: This is the first and most important thing when sizing or fitting a cross country ski because skis have different stiffnesses. The stiffness of a ski will determine how the ski behaves under the skier.
2) Skiers Height: Longer skis are naturally stiff because of the amount of material used in their construction. So often the skier's weight will dictate the length of the ski, but if given the choice of two lengths the skier's ability should be considered.
3) Skier's ability level: Longer skis are generally faster but can be difficult to control or maneuver for beginning skiers.

"Where do you plan on skiing?" This is an important question when determining the correct ski. Do you plan on skiing on frozen lakes, snow-covered golf courses, or in the woods through fresh ungroomed snow (waxless classic is your best option), are you planning on skiing on machined groomed trails at a ski area or local park? (skate or classic)

Skating: "skiing in which the skis are pointed outward and the skier alternately pushes off one and glides on the other in a motion similar to ice skating."
Skate Skiing must be done on machined groomed trails.

Classic: "skiing in which the skis are alternately pushed forward parallel to each other in a motion similar to walking or running."
Classic skiing can be done on both groomed and ungroomed snow, but different types of skis will be performed better in each condition. A racing classic ski, which is long and narrow will be faster in machined groomed "tracks" but may sink under fresh snow and be slow and difficult. While a touring or waxless classic ski that is wider and short will be more efficient in fresh ungroomed snow but may be slow and cumbersome in machined groomed tracks.

Classic and touring skis are fit at a different stiffness than skate skis because a classic or touring ski needs to have both good glide and kick.

Waxable Classic Skis
A Waxable Classic ski can be used in all types of snow conditions and when waxed properly will be the fastest and most efficient option. Waxable Classic skis use kick or "grip" wax on the base of the ski under and in front of the skier's foot (kick zone) and glide wax on the tips and tails. Most Nordic ski racers prefer to use waxable skis because it gives when the ability to make an adjustment based on snow conditions and temperature.

Waxless Classic Skis
A Waxless Classic ski is a popular option because they do not require a lot of maintenance to perform efficiently. A waxless classic ski may use a fish scale or crown pattern or skin material in the "kick zone" which allows the skier to grip the snow and glide the other ski forward. Waxless Classic skis provide grip in a variety of snow conditions, making them the best option for the skier who wants to "grab and go" and not worry about waxing.

Note: You can still wax the glide zones of your waxless classic ski with glide wax, this will allow the ski to glide faster and further.