Mine's changed a bit - used to be shoulders, but now I have to go a bit lower, the skin won't tent as well anymore due to increased hydration so its between shoulder blade and elbow, when sitting/laying down, and in the back end, between the hip joint and the *dip* - if your baby is laying with their hip cocked off and back legs tucked up abit, find their hip joint with your fingers, then "walk" your fingers 1 - 2 inches towards the curve of their belly. You should fell a "dip". Pinch around there, up towards the spine, down towards the joint more, etc. Within a 2-3 inch radius and you'll find, usually, a really good tent place.
You should feel the resistance of the needle going in - push just a little with your hand, make sure the needle is seated - then slowly plunge. Slowly pull the needle out - keep the skin tented, once the need is out, using your fingers of your syringe hand, rub lightly around where you injected. You should feel NO wetness - slowly let the "tent" go, and lightly rub, pet/stroke the area for a few seconds. Voila!