What position should we adopt when we pray to God? -- David 

Here are some passages for you to consider.

Kneeling: 1 Kings 8:54, Daniel 6:10, Acts 21:5
Standing: 1 Samuel 1:26, Matthew 6:5, Mark 11:25, Luke 21:36
Lying: Mark 14:35, 1 Corinthians 14:25
Sitting: Judges 20:26 (in the NIV, and I see that the Hebrew also uses the word “sit,” though it does not appear in all translations)

The most common position in ancient Christian art shows a man or woman standing, with arms outstretched (hands lifted—Psalms 63:4 etc).

Of course the Bible emphasizes the inner disposition of the heart much more than the actual position in prayer. See Matthew 6.