Not in any particular order
1 Breasts
The breasts are really a hard one for me.It mostly has to do with how you need to account for gravity as well. There not just floating and staying still all the time. They move depending on the gravity and the pose. I try to picture them as water balloons wrapping around the rib cage. That helps me alot.
2 Fingers
The fingers . We all saw it coming from a mile away. Yes I have trouble with the fingers well. There so complex.When trying to draw them I simplify the base of the hand as a sqaure. Then draw the figures as little cylinders. Even with that there still complex as heck my dude.
3 Feet
The feet. Honestly for the same reasons for the hands. The base of the feet are somewhat easy but the toes are what really get me. Again I try to image them as cylinders.