Drawing breasts. How to position breasts.
Drawing realistic looking breasts.
How to draw Breasts.
When drawing breasts it is important to note that as the body changes position, the breasts do also.
The breasts sit over the pectoral muscles, consequently, any movement of the upper arms and upper body will alter their position. In fact, the breasts constantly change position because of any change in posture. The sketches below show the position of the breasts in relation to the position of the subject's body.
How to draw breasts with the subject in a seated position.
The first sketch shows the model in a seated position. Her arms are by her side with her hands placed on her legs. The breasts sit naturally on the chest and the nipples are facing forward in a neutral position.
How to position breasts when the subject leaning back.
The next sketch shows the model bending back with her hands behind her back. The muscles of the chest and shoulders have drawn up the breasts causing the nipples to lift up also. Note also that the stomach flattens and the rib cage becomes more prominent.
How to draw breasts in a more natural position.
In these sketches, the breasts are sitting naturally on the chest. Note how the movement of the arms affects the position of the breasts. See how by raising an arm the breast lifts higher on the chest drawing the nipple up and out.

How to draw breasts when the subject is leaning back on one arm.
In the sketch of a seated nude, you can see that by leaning back slightly on one arm the breast rolls back also. The nipple points out slightly and the breast flattens into the body.
How to draw breasts when the subject is laying on her side.
In the example of a nude lying on her side, you can firstly see that she has larger breasts. Her breasts, due to their size hang from her body and the nipple points slightly to the floor as the weight of the breast draws the heaviness down causing the tissue and tendons in her chest to stretch to support the breast.
All of the examples above are intended as guides for you to use and reference for your own life drawing projects. 
Proper nipple placement and positioning when drawing breasts.
Now we are familiar with the different types of breast and how they look in various positions it is now time to consider how the nipples should look. When drawing breasts the placement of the nipple is important. If it is placed in the wrong position the whole breast looks completely wrong.