Holding the tourmaline under cold running water will release any negativity it has collected. You can charge it it too, sunlight is good for this. If you really want to go to town you can also programme the cleansed, charged stone. Sit quietly with the stone in your hand. Focus on your intention that it protects you from negativity and breathe your intention into the stone. You will feel when the programme has 'taken'.
Stones can do their job pretty well without charging and programming, they work according to their nature. That's why I just get people to cleanse in general, but by taking the extra steps they can work in a more focussed and effective way.