1) If you just cannot avoid extra-marital sex in India, FOR HEAVEN'S SAKE, USE THE CONDOM even if the other person is not a commercial sex worker. See AIDS in India.
2) If you are male introduced to a lady or a grown-up girl, don't take the initiative of offering a handshake. If she extends her hand, you must reciprocate, but don't be the first to extend your hand. If you are female and are being introduced to a male: it is up to you – the female – to take the initiative for a handshake. The rule of thumb is: the female extends her hand first, and the male reciprocates.
3) The Western practice of a peck on the cheek as a form of greeting a lady or a grown up girl is JUST NOT IN when you are in India unless you happen to be in 'Westernised Indian' circles or in the company of people in the glamour industry such as models and beauty queens (even then, DON'T take the initiative if you are male).
3) The namastay is a local form of greeting. It involves the joining of your palms as during prayer in church – well, not exactly, but it can pass (in church, the two thumbs are crossed, in the Indian 'namastay', the thumbs join but remain parallel to each other: this is only for information as the difference is not visible to the person in front of you).
4) If you find the lady is not extending a hand shake, go for the namastay. Even with men, the namastay can be an excellent little PR gimmick! Follow it up with a kaise hai (how are you?) and you have broken the first block of ice if one there was!
5) Politics can be freely discussed in India and most people will have an opinion which they will not mind being contradicted. But avoid discussing religion, especially with Muslims who form 11% of India's population.
6) Avoid visiting Kashmir in the extreme north as well as areas in the extreme north-east. Foreigners, especially West Europeans ands Americans, are at risk to hostage-taking by terrorists in those areas. The rest of India is safe haven for everybody.
7) Don't trust strangers with money. Trust your hotel, but not people you may bump into on the streets.
8) If somebody has invited you home for dinner, carry with you a box of sweets or at least a chocolate bar for the kid.
9) If you are buying from roadside stalls or hawkers, bargain you must. Start by offering half the price they ask for and settle for 60 per cent. Don't bargain in proper shops especially those that display "Fixed Price" signs: that will be seen as bad manners.
10) Never buy food from roadside stalls or mobile canteens. Not that they are bad, but your system may not be accustomed to such delicacies and you might end up spending more time in the loo than normal.
11) Drink bottled water only. Even many Indians who have lived out of India for a few years sometimes suffer stomach upsets on drinking local tap water. If there is no alternative to tap water, ensure it is boiled.
12) Don't offer bribes to get any job done. Bribe-taking and bribe-giving are a common practice in India but they are intended to speed up things or win a favour that you are not entitled to. Plan well in advance. Use consultants or trade and industry associations. If you expect favours, let them come free or not at all. Warn anyone (even in government) who asks you for a bribe that you would report him to the Anti-Corruption Bureau or the nearest police-station. If he persists, do it discreetly so that he can be caught red-handed.
13) Indian English has its own delights especially to foreigners of English nativity. Don't show amusement at the different Indian accents and choice of words. This does not take away from the fact that many Indians speak and write better English than many native English speakers.
14) Many Indians are in the habit of shaking their head in the course of conversation or taking instructions. Don't show amusement if you witness this.
15) Avoid offers of spiritual salvation and magic remedies from saints, godmen and quacks. There may be some spiritually elevated people in India, but there is no way you can distinguish the genuine ones from the crooks. If you are seriously interested in these aspects of India, take help from someone you know or visit one of the respected spiritual organisations in India.
16) Avoid driving in India unless you have been trained on Indian roads.