I need help determing the dimensions of my snowboard?

i've been snowboarding once and really enjoyed it, so much that i am considering purchasing a snowboard so i can return to the snow. i'm basically a first time rider...i can do the 'falling leaf' aswell as the 'S' when going down the mountain....my question however is.....what should the dimensions of my snowboard be? my height is 175cm...my shoe size is 12, my weight is 65kg. any sugestions on brand, length, width ect would be much apreciated. thanks