The key to doing the kangaroo position is to place baby's bottom in the middle of the sling, so that the front of the fabric could reach his chin. Be sure his bottom is lower than his legs. Use the outside edge of the tail to tighten the sling up in front of him. If he is very active, or seems uncomfortable, you may both enjoy the hip position better.

PS. I've practiced on 4 of my own and hundreds of others-that's why it looks easy-but when I started I only knew one position-the cradle(link).