rigging in blender for mecanim

Hello! I'm having some trouble getting my game character to work with Mecanim. When I create my Avatar and add animation to it it collapses to a little ball of arms, legs and body.

I guess I have rigged my character wrong, or picked the wrong bones setting up my avatar.

Is there anywhere I can go look to find out how to rig and name my bones correctly in Blender? Or do any of you have some advice?

Any help much appriciated