This is a difficult topic, especially for woman. India is changing in the sense that the newer generation is adapting more to the western style of clothing, while the older generation still sticks to traditional clothing like the Sari. As a thumb-rule, one can typically say that in the big cities, jeans and a t-shirt are perfectly fine.
For men, long trousers with a t-shirt or blouse are fine. In the big cities, shorts are also acceptable. In every scenario, flip-flops are ok, unless for a work situation, where, black official shoes are worn, a pantalon and a long sleeved blouse. Usually no tie or jacket as it is too hot, unless the meeting is very official.
Too revealing clothing such as, shorts, cleavage too short skirts is still frowned upon. The thing is also that typically, Indian man tend to stare a lot to woman, especially western woman, and especially when wearing revealing clothing. When you balance the pro’s and con’s, it is usually preferred by many woman traveling through India, to be comfortable in your close and your surroundings. Also, because, unfortunately, for woman it can still be dangerous. If you take a look at the Sari, the most important area to be covered are the legs. The midriff is usually exposed. Arms and back exposure is usually not a problem too.
So what is recommended?
- Long/light travel pants
- T-shirt (not see through or with cleavage)
- Long skirt (over the knees)
- Colorful clothing
Or if you are feeling adventurous, try a traditional Indian Sari. Also, it is recommended to carry a scarf with you, to wrap around you if you would like to visit holy places or feel uncomfortable. Note that in the big cities, the younger generation do wear things as little black dresses etc., so the whole can be somewhat confusing at times.
When it comes to footwear, the Indians usually wear flip-flops when outside or ‘formal’ shoes when at work. Note that when you choose to wear flip-flops, your feet will get dirty, and we mean Dirty with a capital D. As for the color, given the smog in the big cities combined with dust and dirt, white/light clothing may not be the best choice.
All in all, best do what feels good for you, but take some long skirts or pants with you, just to be on the safe side.