The safest positions for babies, preemie and full-term, is on their backs. This position reduces the risk of suffocation and sudden infant death syndrome. Contrary to what some people think, putting a baby on her back does not put her at greater risk for poor sleep, choking or getting a flat head. Some preemies with health problems, for instance lung trouble, may need to sleep on their sides, but unless your baby's doctor has given you specific instructions to the contrary, you should position baby on her back.
Dress your baby in a warm sleeper before putting her down for the night, as you should not cover babies with blankets while they are sleeping. Do not overdress her or overheat her room. Remove all blankets, pillows and toys from the crib, as these pose a risk of suffocation.
Place your baby in her crib on her back, being careful to support her head and hips as you lower her into it. Make sure all limbs are free, with clearance on every side and nothing trapped at an awkward angle or underneath her.
Reposition your baby every so often to prevent her getting sore spots or flat or elongated spots on her skull, which is a risk with premature babies.