whatever you do in new delhi, just be a bit aware of things.
1. you CAN get robbed if you're not careful, as well as conned.
2. if you give money to 1 begger at a red light, chances are if you give it at the start of the red light, there will be over 9000 more beggars. try to avoid such a scenario.
3. if you go to south delhi, make sure you go to a place called "Evergreen". trust me, you will like the food there.
4. south extension is good for shopping.
5. gurgaon (outskirts of delhi) has alot of shopping malls if you fancy shopping. personally, considering that you've lived in the UK, had i been you id avoid malls and go for the more traditional/cultural stuff, seeing as you can get the stuff like malls here as well anyway.
6. see if you can go to a place called Dilli Haat (thats how its pronounced) for cultural stuffs.
7. avoid drinking tap water, your stomach might not be able to cope with it. try to go for bottled water.
8. if you get a chance, it may be a bit cliche, but you could try to go to aagra and see the taj mahal. theres also the lotus temple (which is quite spectacular tbh), and if you fancy going to some religious temples, try the sikh temple called "Bangla sahib" (since im sikh, its the best recommendation i can give). qutab minar, humayun's tomb, asiad village, habitat center are some of the sights you can go (infact, i think you'd like the habitat center).
problem is, alot of things have changed in New delhi ever since i came to leeds, so i cant really give a better idea. this is the best i know, places and experiences i had when i used to live there, so its best i can suggest.
also, some hindi words you might want to learn if you speak to people there:
Namaste = hello/goodbye.
Dhanyavaad = thanks alot
mera naam andy hai = my name is andy
Kithne paise hooey = how much money is that then?
and if you meet a sikh, try saying "Sat Sri Akaal" to him/her, which means hello in punjabi.
Hope this helps you some-some.;)
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edit: regarding food in india, depending on how long you stay there, i guess it can take you sooner or later to get used to the food. if you stay in india for say.. 2 weeks, for the first week, id say avoid too much exotic foods. STICK TO BOTTLED WATER ALL THE TIME, that will really help you. if you're going in the summer, make sure you take loads of "airy" clothes, because it -really- gets hot. lets just say you may go there white, but you might come back browner than me.:P
you HAVE to try gol guppas and jalebi's at evergreen if you get a chance though. they're quite amazing.
Erm, make sure you go before you set off, you'll need your thermos of tea & sandwiches
wraped in tin foil, a sleeping bag because it can get cold in the back of the van on the way
to luxemburg, make sure you do your smoke in before customs! those dogs have got it sussed,
no running around the pool, no petting or bombing.
Oh and keep doing those exercises with your feet so that your arse doesn't go numb.