Once I know roughly where I want to go the first step when planning a trip is generally to book the flight.
We decided on going to Rajasthan, therefore it made sense to fly into and out of Delhi.
After looking at the prices of flights in July 2008 for March 2009, it seemed the cheapest and best option was to fly Finnair from Heathrow to Delhi via Helsinki. Cheap, yes, but 14 hours with a delay in between. The direct routes were much more expensive although only took 8/9 hours.
Once we returned from 2008's holiday it was time to look at booking the flights. Luckily both Virgin and British Airways had a sale on, 25% off, bringing their price down to a hundred pounds more than Finnair. The timing of flights on British Airways didn't really suit us, whereas Virgin fly out at 10pm and return at 5pm effectively meaning one extra day in India for the same price and time off work/school.