When we practice meditation we need to have a comfortable seat and a good posture. The most important feature of the posture is to keep our back straight. To help us do this, if we are sitting on a cushion we make sure that the back of the cushion is slightly higher than the front, inclining our pelvis slightly forward. It is not necessary at first to sit cross-legged, but it is a good idea to become accustomed to sitting in the posture of Buddha Vairochana. If we cannot hold this posture we should sit in one which is as close to this as possible while remaining comfortable.