You'll find tasty recipes for Mutton Biryani everywhere! I guess the main point you must remember is , to cook your rice in such a way that it still remains loose after being cooked.. this way, the flavours of the spice is evenly spread in the whole Biryani.

Serving with Masala Papad would be nice.. Masala Papad is with spices and finely chopped tomatoes and onions on top with a bit of fenugreek leaves, and lemon squeezed on them.. ensure that the papad is fried and the oil is filtered using tissue paper.

Try this: http://www.food.com/recipe/indian-mutton-biryani-59380

or best, the master himself:

http://www.sanjeevkapoor.com/gosht-biryani.aspx