Determine how much time you have to spend in India. An is example is how to work a typical two week, 10 working day vacation is to try to fly out on Friday afternoon or night at the end of the week, arrive on the following Saturday, and to then depart on the last Saturday and return on Sunday. Excluding travel time and minimal jet lag recovery, this grants 13 days on the ground.
Establish your entry and exit points in India. Most visitors fly in and out, and if a lot of ground is covered, it may be better to plan a triangular flight, multicity flight where you enter and leave from two different cities. These are usually more expensive, however, so other options are to book your own connection back to your exit point by using a budget Indian airline, to keep close to the central entry/exit point and double back, or to plan a route that is circular and returns to the entry/exit point.
Use your travel guide, and note how to get in and out of where you may potentially want to visit, and how much time it takes to do that travel. Point-to-point travel time is vital in planning a route.
Make a rough estimate of how much time you anticipate spending on doing the things on your itinerary. Be liberal in making this estimate: if you think you will spend one hour at the Taj Mahal, plan on spending two.
Take a map, a pad and a pencil and start planning point-to-point travel time and time spent in different locations for each day of the trip.
Start subtracting attractions if you are over budget. If you are severely over budget, rethink the entire route. If you are under budget, start adding attractions.