The easiest way to position baby in the sling is to untie the knot and lay the sling open on a beanbag (A great beanbag is the Newborn Nest and can be purchased at newbornnest.bigcartel.com). Lay baby in the sling and position them while on the beanbag, either on their tummies or on their side. I suggest positioning the baby on their bellies with their feet tucked/folded under them and their arms folded underneath their chin. The trick is to have one arm slightly outside of the sling resting on the support bar and the other arm inside of the sling. Position baby more towards one side of the sling than the other so that you can use the side of your sling to support the baby’s head and keep it snugly inside the sling. Once baby is positioned nicely bring up the sides of the sling and gather them where you will tie the knot. It is important to gather more from the back of the sling so it does not sag down from baby's weight. Keep a tight grip on the fabric and lift the sling a couple of times to make sure the position is going to hold. Do this several times before actually lifting baby to ensure baby is snug and safe inside the sling. Once you are sure baby is snug tie one knot where you have gathered your fabric without losing any slack (if this is difficult have your assistant or the parent help you). Once the knot is tied have your assistant slowly lift the baby a few inches above your beanbag with one hand under their bottom and one hand under baby's arms (you will need to clone out the beanbag and assistant's hands later in Photoshop). Always have the parent keep their hands on baby. The baby’s safety is your first priority so please never suspend too high above beanbag - you should be able to see the beanbag in your shot. Tie your sling to a sturdy port-a-stand and have parents keep their hands supporting baby at all times (see below). Edit hands out later in post processing.
Safety First: Only use the sling on newborns 12 pounds or less and only if the baby is good and sleepy. I recommend not using the sling if the baby is having trouble sleeping and likely to move around. ALWAYS have a large beanbag directly underneath the baby while working with the sling.