How do I avoid dry meat and burned masala and rice in biryana?
Most people get burned biryani because of the rice. It must be soaked and the par cooked
before going into the pot. Also the quality of the rice is important. IMO that would always
be Basmati rice. I always soak my rice for an hour for any dish. 
The cooking vessel has to be heavy and sealed. This ensures that the cooking happens
in an almost pressure cooker state inside the pot. Some people seal their pot lid with
a flour dough. Cast iron pots are the best.