First of all, just start like any other language. Learn the basics and work on your vocabulary. Then you can join Chinese Skypecasts for example. I'm not that good at Chinese yet, but there's no harm in just staying in the listening part for a while to get used to the speed and way they speak. Some people are easier to follow than others. Hehe, one time this guy was in some kind of extremely long monologue. Quite intimidating. 哈哈
Oh, and of course you can try and find language exchange 朋友 here to talk with. I'm sure there are Chinese people here who would to practice with a British guy. (Hehe, don't make them sound too British, okay?)
Aye, mate. Good luck!