Visitors are not to be expected to tip taxi drivers. However, hotel, airport and train station porters should be tipped approximately Rs50/bag.  If a service charge is not included, tip guides Rs 200 and drivers approximately Rs350 per day or 10 percent where appropriate. In restaurants, if the service was good, tip anything between approx 5-10% of the bill. Depending on the category of the hotel, and the bill amount. It's not mandatory, you may not leave a tip if you don't want to. On receipts, it will often say "Service Charge." This is NOT an automatic tip charge on your bill. It is a government issued tax that has nothing to do with the service your waiter provided you. 


Delhi is not a highly conservative city. But while traveling in certain places like Old Delhi, it is better to dress conservatively. One should not try to attract a lot of attention towards himself/herself due to his/her dressing style. This often attracts unwanted attention. When entering temples, mosques or buildings of religious importance always check what dress attire is required.  In most cases you will be required to cover your head, take off your shoes and be dressed conservatively. Its always a good idea to inquire first at your hotel or with your guide about the dress codes (if any) of the places you will be visiting before you set out. Please keep your mobiles in silent mode when you are visiting such places. Also public display of affection is not recommended. Public display of affection is bound to attract attention. People will stare. That is a reality. The best way to tackle is to smile back. But do not encourage / indulge everyone in a small chat. Some are just curious, while others may try to get too familiar. Keep your distance unless you get a great vibe or he/she is known to other known people.  

People understand and give a certain leeway to tourists, but it doesn't harm to respect local customs. 

Be respectful towards seniors.