Ready, set, sari! Millions of people and styles. Here's my glo-guide and what I found most helpful when packing for traveling around the Delhi, Uttar Pradesh, Rajasthan, Maharashtra regions.
In the larger cities, women wear western style clothes (western meaning “NY/LA”, not “John Wayne”). Stomachs and shoulders are okay, unless you are going into certain temples/religious sites. As badly as I wanted a sari (the beautiful, colorful wrap dresses), I did not buy one. I knew I would not wear it again and decided to save my money for gifts.
Fabric stores are plentiful and the textiles are breathtaking. Word of warning, I strongly advise against having garments made in India. Unless you know the shop or have time to spend on multiple fittings, the outfits probably won't turn out well. I spent 4 times as much having mine altered when I got back to the states. I would recommend buying the fabric and brining (or shipping) it home.
Be cautious, if you dress in very nice clothes, you will definitely stand out as a tourist and approached more often.
Don’t be afraid to hand wash and re-wear clothes while you are there. This will save space in your suitcase. You can always change up the outfit with accessories and scarves. I just used body wash (and towards the end of the trip, shampoo) and it worked great!

Tops
Light, layer-able shirts - I would recommend 1 shirt for 2 days wear (depending on your activity)
One light jacket, preferably waterproof incase of monsoon rains
If you are traveling in the North, you may need a heavier jacket or long sleeves
Pants
Leggings, jeans, or loose, breathable pants - I would recommend 1 pair for 2-3 days wear (depending on your activity)
If you take a yoga class (recommended), don't forget loose-fitting workout clothes.
I bought several harem pants before I left, this was a mistake. I could have bought them at local markets for much less
Maxi skirts and dresses - I got the most use out of these
Shoes
Flip flops - At least for the shower/wet bathrooms (where the shower and toilet are in the same room so the floor is often wet). I had a shoe blowout and ended up wearing flip flops the whole trip. At first I was worried about what I would step in on the streets, but they ended up being the easiest things to clean.
Comfy, closed toed shoes you’re not afraid to get a little dirty. I have a pink pair of converse that go on every trip with me.
Shoe Tip: There are so many awesome leather shoes and sandals you’ll want to buy. You absolutely should but, unlike the scarf, you’ll want to break shoes in before wearing them all day. One bad blister can ruin the trip.
Shoe Tip 2: I have very large feet (size 10 US women's). I did not find a single pair of shoes that fit. It was quite comical trying to 'Cinderella' my giant feet into Indian shoes.

Accessories
A (single) scarf - Don’t go overboard here, you’ll want to buy scarves and fabrics once you’re there but I always like to bring a comfy scarf for the plane ride.
Health/Toiletries
Malaria medicine
Broad spectrum antibiotics
Asprin/Advil/Tylonol
Antihistamine, anti-allergy, motion sickness tablets
Band-aids
Insect repellent - Don't forget to apply at night!
Sunscreen
Tums or some sort of antacid - even if you don’t get sick, these will help settle your stomach with all the rich foods and spices
Electrolyte mix or oral rehydration mix - for the inevitable Delhi belly
Hand sanitizer
Body wipes - Between the heat, humidity, and dust, you’ll want to shower every few hours. This isn’t realistic so wipes will be your best friend.
Travel toiletries (toothpaste, shampoo, conditioner, body wash, lotion) - Most hostels/hotels/AirBNBs will not include this.
Dry Shampoo - See “Body Wipes” explanation above.
Other
See Golden Rules - What to Pack post
The converter you need is Type D. I ordered mine from Amazon.
India requires a visa to enter the country. If you are not going on business and are staying for less than 6 months, you'll need an eTourist Visa (visa blog post to come).
Travel Insurance
Photocopies of important documents (visa, passport, credit card, tickets, etc.)
Hotel address and contact info written down. You can show this to the taxi stand or tuk tuk driver (if they don't know where it is or can't read it, they will probably pull over and ask someone off the street - true story)

Best advice, you can buy almost anything (except your passport) in a local shop. Don't sweat it (just sweat the heat while you're there)!