This is what I think would be perfect for a 3 day Hyderabad trip. You should reserve one full day for Ramoji Film city. On the other 2 days, you can see: Golconda fort (don't miss the light and sound show in the evening even though there are a lot of mosquitoes)
Salar Jung museum
Hussain Sagar Lake
Birla Science museum (It has a huge dianosaur skeleton)
Snow world (it fun time)
Birla temple If you are a non-vegetarian, go for Biryani and kebabs - Paradise or Bawarchi. Karachi biscuits, sandwiches and pizzas at Pista house near Charminar.
Best to do would be: Ramoji film studio, visit falaknuma palace, chowmala palace, hussain sagar lake and char minar. do not forget to buy pearl. hyd get good cultured pearls in best Price. my suggestion not to waste time on visiting gardens and zoo. must try paradise biriyani!!!!! delicious