...really depends on how long and what you are interested in. First time I had no fixed time limit and no real plan except I thought Hampi looked good in the Lonely Planet and I didn't want to arrive in any big cities (!) so flew in to Chennai. Ended up:
Chennai (2 days), Pondicherry (two weeks) - side trip to Tiruvanamalai (SP?) (three days), Bangalore (two days)
Hampi (two weeks), Panaji (two days), Anjuna (two weeks), Margaon (two days), Jalgaon (for Ajanta Caves) (three days), Pushkar (two weeks), Jaipur (two days), Agra (three days), Varanasi (three days), Bodhgaya (one week), Calcutta (one week).

I might have missed something there.

Second time had only 28 days, so planned a bit more carefully: Mumbai (four days), Aurangabad (for Ellora caves) (three days), Sanchi (four days), Fatehpur Sikri (four days), Jaipur (two days), Pushkar (three days), Shimla (four days), Delhi (three days).

But it's up to what you want to see, what you're interested in experiencing and allowing enough flexibility that you can stay at places that are more interesting than expected etc.

Good luck and enjoy.