Blanch the bones for a few minutes in boiling water and skim the foam (optional but can help with off taste) make sure to roast the bones in the oven for a few hours before making the broth for increased flavor. Most importantly, once the broth starts to cool skim all of the fat and use that for tallow. Bone broth should have no/minimal fat depending on taste because lots of liquid fat will make most people nauseous.