There are several different leg positions that are possible while seated this way. The first and simplest is the Burmese position, in which the legs are crossed and both feet rest flat on the floor. The knees should also rest on the floor, though sometimes it takes a bit of exercise to be able to get the legs to drop that far. After awhile the muscles will loosen up and the knees will begin to drop. To help that happen, sit on the front third of the zafu, shifting your body forward a little bit. By imagining the top of your head pushing upward to the ceiling and by stretching your body that way, get your spine straight - then just let the muscles go soft and relax. With the buttocks up on the zafu and your stomach pushing out a little, there will be a slight curve in the lower region of the back. In this position, it takes very little effort to keep the body upright.