I am not a proponent of co-sleeping, because I'm very afraid that a parent will roll over on top of a baby, or a blanket will be pulled over a baby's head. I have also had patients who have fallen off the mattress, despite parents reassuring me that the baby is fully protected, and will not fall off the bed.
Parents can buy co-sleepers, which go adjacent to the parents' mattress, and you can also put a bassinet, or pack 'n play right next to your bed. In addition, you can keep a crib right next to your bed so you can always see your baby.
Different cultures approve of co-sleeping, and that is fine, as long as it works for your family.
Babies should always be put to bed on their back. Babies should always be put to bed in a crib or a bassinet. I do not recommend parents holding their babies to fall asleep, or always putting a baby in a stroller, or in a car-seat to fall asleep.
Sometimes that's just taking the easy way out, because the babies will fall asleep when they're in a stroller, because of the vibrations. It's almost like being back in the womb. And a baby will fall asleep when the parents are holding them, because it's cozy and warm. The problem is that when your baby wakes up, and they're not in their parent's arm, or they're not bouncing along the road in their stroller, they cry and they wake up because that wasn't the situation that they were in when they were put to sleep.
I recommend that a parent feeds their baby or nurses their baby and then lays the baby down while they're in this kind of almost sleep state, and the baby learns to sleep on their own.
At nap time I also recommend that parents put the baby down while awake, and the baby learns to console themselves and soothe themselves to go to sleep. This might take a pacifier, or the parents might have to put on some soft music.
When a baby is a newborn I recommend that the parent leave the house light during the day, even if the baby is napping, so the baby learns the diurnal day/night cycle. I always recommend leave the lights on during the day, and at night-time, keep it dark, so the baby starts to adjust to your schedule.