How does one perform the Night Prayer (Salat al-Layl) and what is the number of its rak'ahs?

The Prophet (peace be upon him) used to pray eleven rak'ahs, and whoever limits himself to that, it is better. But whoever adds more, there is no harm in it, for the Companions used to pray twenty rak'ahs, and this is the opinion of most scholars, such as Al-Thawri, Ibn Al-Mubarak, and Al-Shafi'i.