Load up a crockpot with bones (especially joints), wingtips, cartilage, whatever you got. I like to add garlic, onions, herbs (thyme, rosemary, basil, oregano, whatever) a little seasalt, some vinegar and 2ater the rest of the way. I usually run it on high for a bit, and then on low for 12-48hrs. I also usually ladel most of the broth out the next day, add more water and vinegar and keep cooking.
If you smoke or roast the bones first it deepens the flavors.