Well, these are the few things that I know of deep-frying
-Dont fill oil to the brim, choose a deep pan and leave enough space in case if the oil bubbles up
-Before adding oil, make sure the pan is clean and dry. Even if one tiny drop of water is left unnoticed, the oil keeps bursting out with it.
-Make sure the ingredient that you are going to fry is also water-free.
-For savouries like Bhoondi, even for Bonda's, they come out in nice round shape only if they have enough oil to immerse.
-The oil should not be too hot for Vada/Bajji/Bonda as the outer becomes coloured soon but inner part wont get cooked well. Always use med-hot for these type of foods.
- Add a spoon of hot oil while mixing batter for Bajji/Pakoda etc..
-Adding rice flour will give crispness, but there are chances that the dish gets screwd up with using too much of rice flour. Check appropriately and use.