Being myself from Pune , Maharashtra, I have seen how the city has grown leaps and bounds in last 5-6 years.
It is a sad fact that Mumbai, our commercial capital , has almost 60% population living in slums.
So to prevent emergence of new slums in our cities ( all over India) :
1) Study the geography of that area and think of Fencing or Limiting its exsistance. For cities that will have Sea or Forest nearby, naturally that will be their limit. Fence the city from outside. Build a Gate or something like Entry Point .
2) If the city is in middle with full scope of growing, declare all the land on the hills as 'Environment-Friendly' land which will have no slums coming up.
3) Many times its observed that political interference in slum development is seen as they see slums as vote bank.Strict Demolition Drive be taken, instead of slums climbing up hills , plant trees there.
4) Where slums are exsisting , provide an alternative housing scheme and see to it that compulsory evacuation takes place.
5) Control Migration into heart of the city by developing the nearby city area so that instead reverse migration occurs.