It was narrated from ‘Abdallah ibn ‘Umar that the Messenger of Allaah (salla Allahu alahi wa sallam) said: “Make your rows straight, stand shoulder to shoulder and close the gaps, and do not resist your brothers’ hands. Do not leave any gaps for the Shaytaan. Whoever complete a row, Allah will reward him, and whoever breaks a row, Allah will forsake him. (Abu dawood)
How to stand in congregational prayer
http://www.youtube.com/watch?v=26iapz_9Q-M