Start with Luke Warm Showers
You must adapt in a progression to the cold, instead of diving right into it. Slowly work towards colder and colder.
2. Making noise
Making the Ohm or Aum sound continuously really seems to shield from the cold. It creates vibration and other unknown forces to work, try it.
3. Toughen up mentally
Use your mind to look at things differently. Imagine something that will be positive and try to really feel that it is real. Imagine you are in a sauna or there is no way you could be cold because its so incredibly hot out.
4. A lot of breathing
Deep breathing and holding the breath is an easy way to help increase your heart rate.