In India, as in several other Asian countries and many parts of the Muslim world, it is insulting to show people the soles of your feet. A casual way of sitting that would be perfectly acceptable in many Western countries would offend an Indian: stretching your legs out in front of you, for example. Keep your feet flat on the floor or, if you cross your legs, make sure you keep the soles of your feet pointing towards yourself.
If you accidentally touch someone with your foot, you must show respect, usually by touching your heart and your forehead with the right hand or with both hands, as in namaste. You should not point at things with your foot (or your hand!) but with your chin. You should take your shoes off when you enter temples, some people’s homes, and certain shops. Do as your host does.