Use good quality ripened mangoes that have fewer fibers.
Add sugar as per taste. Also, taste mangoes first and then add sugar accordingly.
Mango mastani served in shops has tutti frutti in it. Add 1-2 teaspoon of tutti frutti to it.
If you want your milkshake to be thin consistency, increase the quantity of milk or decrease the quantity of milk for a thick milkshake. Tastes best when served chill.