What are some things that makes a good don/boss ?

I could say what is not to do, to be a good boss:

Be a petty and greedy boss as Profaci;
Use the murder as the only answer as Scarfo or Casso and frighten so much your men to flip for avoid to be killed;
Attract too much attention, blaming others and continuously badmouthing him (Gotti case);
Know when it's time to hand over power and don't start a war just because you want to keep control from prison through his family of blood (Persico).