1)Use good quality basmati rice you can afford.
2)Soak good quality rice for atleast 30 mins to 1 hour. The longer you soak the more long your rice will get.
3)Use lots of fried onions. Fried onions adds nice sweetness to the biryani.
4)Cook basmati rice just right. Always stay near it and cook till done. Remember that the rice will continue to cook as it is in DUM.
5)Use good quality ghee for the aroma and add it after the biryani is cooked.
6)I cook my biryani in coconut oil for best taste.
7)Use large heavy bottom pot for the dum part. Place the pot on lowest heat possible. If you are too worried, you can place the pot over a tawa and cook.