Submit your entry (in .jpeg image format) to email@example.com with Guild Wars Wintersday Art Contest 2010 as the subject line. You can also enter via snail mail, and the address as well as the complete contest rules are available on the official Guild Wars website.
So what do you get for your trouble? The top three entries will receive a Razer Carcharias gaming headset. Seven second place contestants will take home a Razer Abyssus gaming mouse, and 10 honorable mentions will get an in-game item (the Everlasting Reindeer Tonic). The entry deadline is 12:00 p.m. PST on December 31st, so what are you waiting for?