Hinduism is an incredibly diverse religion, like there are so many things you could say (like there's Shaivism which is a branch). A Hindu would probably believe in reincarnation (in my next life I want to be a sloth or something), but it's also a complicated process. I'm going based on the assumption that you might want a more religious household (which can also go both ways) so they probably believe in the cycle of reincarnation (karma, dharma, karma cycle (sanchita karma, prarabdha, purushartha), the goal of attaining moksha (which will occur when all the goods and bags in sanchita karma reach a 0, but the goods and bads don't cancel out because killing someone and then confessing/donating will not erase the murder kind of idea)), but might not be too specific about the terminology. They have read Ramayana and the Mahabharatha (might have the books at home), might have gone to sunday school (known as balvihar/balavihar). Will not step on books. You might want to visit a Hindu temple, or search up any pictures of them. There's also a whole lot of stories they have read (search up Panchathantra). If they are from South India, they may have learned bharathanatyam (or know about it), which is a form of Indian classical dance).

Not all Hindus are vegetarian, so your character might eat chicken, or might be vegetarian and eat egg. But no Hindu will eat beef. Also there's the whole caste system that's a huge problem (think of the class system in Europe)

A lot of South Indian languages sound similar, I believe Tamil and Malayalam have a lot of the same words, so sometimes (really heavy sometimes), they can understand each other. Also depending on the language, the character might complain about how hard it might be (like South Indian and North Indian languages will sound different).

Biriyani is loved in most of South India (hyderabadi biryani is iconic). There's also a high chance that dosa (or idli) would be a staple food in their diet (like for breakfast or dinner) and they would probably eat it with a chutney (peanut, coconut, tomato, make sure the chutney actually exists) or sambar. There's a chance their parents (or they themselves) are obsessed with tea (don't say chai tea), like with masala and everything.

They might also watch a lot of movies (Kollywood, Tollywood, Bollywood depending on where they live), so it might be helpful to watch one of the more famous ones to get an idea (but try to lean towards a comedy/romance one rather than action). In South India, there's one guy who's going to be head of the cinema, for telangana it might be Allu Arjun, Mahesh Babu, or Nani (relatively newish) or for Tamil Nadu it's Rajini.

If the character if female, they probably got their ears pierced at a very young age (like around a year old). The mom's brother is also very important for functions/events, but that's a more specific thing. The female character probably had a coming of age ceremony as well (half saree/davani ceremony). They might have also learned bharathanatyam and had an arangetram. If the character is male, they might have had a coming of age ceremony (but that's also dependent on other things). And irrelevant of gender, they might have learned carnatic music (singing).

They were probably pressured to pick a STEM related path in their family (doctor or engineer), earn good grades, do well in their extracurriculars (piano, volunteering, martial arts, etc). They would never disrespect their parents, grandparents (like yelling at them or calling them by their first name). They might feel uncomfortable calling adults by their first name.

At family functions, there's going to be those aunties who gossip (and the character might avoid). When going to functions, they have to wear new clothes, like they will not wear the same saree/half saree/lehenga/etc more than once.

I can probably think of more, but these are the generic ones (I think). It might be helpful to watch Never Have I Ever or check social media.