Like most countries, Indian food is quite different depending on the region from which a particular dish originates. In general, however, the key to Indian food lies in the proper use of spice blends. Rather than overwhelm and dominate the dish, the spices lean more toward enhancement and subtlety. Other generalities in Indian cooking seem to gravitate toward milk products such as clarified butter (ghee), or curd (dahi). You'll also find broad use of lentils (dals). This is where the regional similarities end, however, as dishes vary dramatically in taste, texture, color and presentation from point to point on the compass.
Northern Indian food is heavily influenced by the Persian ancestors from the area, stemming from the invasions (and subsequent rise to power) by the Mughals in both the 11th and 16th centuries. Arriving with the Mughals were Persian and Afghan cooks, specializing in such dishes as pilafs and biryanis accompanied by braised meat simmered in cream sauce (kormas), spicy grilled meatballs (koftas) and kababs. The Mughals introduced a new method of cooking to the region, using clay ovens called tandoors. Yep, you guessed it; that's where we get tandoori chicken. Many northern Indian dishes also showcase chapatis or rotism, which is unleavened bread baked on a griddle. You'll find a variety of dishes containing lentils, fried vegetables, chutney, curries, pickles, and curd. Wheat is a staple for the area, so breads are popular as well.
By contrast, Southern India tends to lean extremely heavily on rice. You'll find rice in everything ranging from the spicy curries served there, to rice pancakes (dosas) stuffed with different vegetables, as well as rice dumplings (idlis). Curries from Southern India tend to be a bit more watery than those you'd find in the North, and you'll find a mix of many different ingredients in a variety of dishes. Mustard, coconut oil, chili, and other spicy seeds can all be found throughout the region's cooking. Most rice dishes will be served with sambhar, rasam, vegetables, and pachadi. You'll find that the majority of South India's food is either roasted or steamed, and is generally less greasy than the other areas of India.
Our third stop on our four-point trip is Western India. Here, you'll discover that the region enjoys a predominantly vegetarian style of cooking. This is in no small part to the Marwari people from Rajasthan. Their cooking is primarily influenced by the warlike lifestyle of the inhabitants of Rajasthan, as well as the availability of specific ingredients. Thus, Rajasthani cooking is characterized by a heavy use of vegetables, a minimal use of water (relying instead on milk, buttermilk or clarified butter), and a longer life than most other foods. Western Indian food is usually very simple, yet rich and spicy. Examples include chickpea dumplings in a yogurt sauce (karhi), spicy potatos known as alloo bhajis, and pooris (a puffed, fried, whole-wheat bread).
Finally, we have Eastern India. Fish! Yes, Eastern India loves fish, and you'll find it in nearly everything. Due to the fact that Eastern India gets lots of rain, and is located right near the sea, you'll find an abundance of fish dishes here. In fact, many rituals depend on a type of fish known as hilsa to be served and eaten. Reading off like a fish menu, you'll find fish grilled, smoked, rolled, made into patties, stuffed into coconuts, and cooked into curry. Many times, fish dishes will be served alongside mixed vegetables in mustard gravy (Shukto). While fish is the staple of almost every dish in the region, you will find rare cases of non-seafood dishes such as Bengali Chicken Curry. This area is also distinctively non-vegetarian. You'll also find that the food in the East isn't served all at once, but is served course by course.
And there you have it. You've probably noticed that each of the four directional areas are distinctively different from one another with regard to their cuisine. Of course, rice is heaviest in the south, but you can generally find it all over the country. The same goes for curry and its varieties. You'll find an infinite amount of varieties and derivatives of the aforementioned dishes, and notice the similarities in all of them. Many people find Indian food to be very spicy, others find it bland. One thing is certain, however; there is quite a variety from which to choose, so the possibility of discovering something you enjoy is pretty high!