Be sure the water is not too hot as hot water tends to stimulate. A warm cup of tea works wonders. There are many varieties of flavored tea on the market today. Try to choose one that is decaffeinated. For instance, Chamomile tea has no caffeine and it has a relaxing effect.
Visualization is used a lot to calm nerves.
Sit back in a comfortable chair. Clothing must not be tight. Try to relax your body. At first, you'll find it difficult to clear your mind but keep trying . Soon you will start to relax.