Keep the soil moist and shoots will start coming up. When the shoots are 4-6 inches long, break them off and bury most of the stem in potting soil. These will root and continue to grow. When these plants turn into longer vines, the tips can be broken off to start more. When the soil warms up, get your garden ready.
Sweet potatoes are grown in long ridges, taller ridges make harvesting easier.
Avoid very rich soil, or your will get lots of vines and no potatoes. I rototill the area as deep as I can, shovel dirt off paths into ridges, then till the paths again. It helps to water the young plants in, but don't worry if they wilt for a short time after transplanting. Control weeds and conserve soil moisture during the long growing season by mulching. Soon you will be unable to see the mulch for the luxurious vines.