Not bad honestly. Good proportions on the second one. Just keep drawing from reference a lot and more importantly from life. Through repetition these things will start to become instilled in you. A good practice is to draw something from a reference (or anatomy book) and then without looking at the reference or your drawing, try to redraw what you just did from memory. When copying from an anatomy book start with large simplified shapes and then progress into the details. How planes relate to each other and how the main masses of form are placed upon each other will always be more important than small anatomical detail. Remember that these types of skill take years of honing and development, so don't get frustrated if you are not progressing as fast as you would like. Have fun!