It is recommended that one pray on their knees for good spiritual reasons. I was taught that this is one of two body positions which shut off the mind, the other being the traditional cross-legged East-Indian position, and Zazen.
Placing the palms firmly together entwines the hand's energy centers (represented by artwork on the palm in some spiritual representations of gods and godesses):
http://i6.photobucket.com/albums/y222/mpeake/Internet/india-goddesses.jpg
When praying, reach upward with your emotions. Visualize yourself reaching upward to the Great Light, and PULL it down toward you and all Creation.
Even if you are angry at God, shouting such is still a prayer, and is an honest prayer. Just don't mock God. Not good.
Combine prayer and the Anapanasati Sutra's mindful breathing techniques.
