Many visitors expecting maharajas and fabulous palaces are shocked when their first impressions are dominated by grinding poverty instead. Prepare for the following:

Attention. Indians will unabashedly stare at Westerners, who are also magnets for irritatingly persistent touts, hustlers and beggars. Beggars, especially malnourished children and the badly deformed, can be particularly disturbing.
Filth. Dirt, garbage and insects abound in the cities. Every wall is a urinal and every field is a toilet.
Noise. Drivers lean on horns, radios and TVs blare Bollywood tracks, even temples use loudspeakers to spread their message.
Pollution. All Indian cities suffer badly. Exhaust combined with dust can make the drier seasons a nightmare for asthma sufferers.

Most visitors get inured quite fast and start seeing the good sides too, but take it easy on your first few days and schedule some time to get away from it all.