You'll notice that this model required an extra set of special bones for the heels (these will be used for skinning purposes)... this is not required for most characters. Feel free to experiment with different models and see how you arrive at an efficient boning solution.

HIPS AND TAIL
Let's start refining the rest of the skeleton. We'll need to create a hip bone, and in the case of this charcater, a tail bone(s). Do this in the front vieport, going from the belly area downwards. When you're done, using the left viewport, rotate them accordingly. You might need to go into Bone Edit mode (bone tools floater) and move some bones a bit, if they're too short. Make sure the root bone is aligned in position with the root bone for the spine chain. They should be located in the same place (their pivots). This will give us a better motion in this area. Here's what these new bones look like...

NECK, HEAD AND JAW.
Create a chain going from the spine's terminator bone pivot point up to the tip of the head. I used two bones for my character's neck, since it's kinda long, and from the character design, it looks like it needs to be able to bend there... and one bone for the head. I then created a smaller bone for the jaw. Be sure to position it in the middle of the model's jaw, and where the jaw bone should be. Check your jaw... your jaw bone's pivot should be just below your ears. My character has a very small jaw, so I positioned the bone accordingly... here's what I ended up with..

CLAVICLES
All that remains, are the clavicles. Create them by selecting the spine's terminator bone, and doing a bone connect operation to each root bone of the arms chain. Select these new bones, unlink them, and rotate them if needed (relinking them afterwards). Here's what you should have...

FINISHED SKELETON

Here's how your finished skeleton should look like now. Take a look at yours and see you're not missing anything. We'll proceed to applying IK solvers, and some special controls.