The culture and festivals in Pakistan display a curious amalgamation of influences that betray the country’s history. Islamic references dominate, of course, but they are spiced with a liberal sprinkling of Greco-Buddhist, Hindu, and Persian influences. This is witnessed not just in the physical monuments that the country prizes as part of its national heritage but also in the intangible points of heritage, such as the local attitudes and religious inclinations.
The first thing to understand about Pakistan is that it is a generally modest country. This should not be taken to indicate that the people are backward or overly sensitive, as many mistakenly understand the phrase “modest” in this usage to mean nowadays, but rather to signify that there are forces that operate upon people here to make them more predisposed to what Westerners would call conservatism. Pakistanis are a rather friendly people, to be sure, and they are not unaccustomed to seeing foreigners in their lands. That having been said, they expect the same courtesies of travellers as most others would expect of travellers in their own lands: a sense of respect for their culture and ways. This means that you should do your utmost to behave and attire yourself in a manner that does not clash with that which they consider decent.
There are some quick codes of behaviour to remember here. Never use your left hand for social purposes better suited to what is considered the more decent right (e.g. shaking hands, giving gifts), do not wear overly revealing clothes (e.g. skirts, shorts, tank tops), do not engage in any physical contact whatsoever with a woman even if it is only a hand-shake if you are a man and not a very close friend of hers, and perhaps most important of all, do not engage in a political discussion. Bringing up issues such as that of the Kashmir or criticising Islam may well get you into hot water.
So much for the more serious part of your preparation. There is a great deal of joy to Pakistani culture too, especially in its holidays. You may not be able to time your visit for the precise holiday you want to see, but you should definitely check which holidays take place during your stay so that you may see them. National festivals are mostly the Islamic festivals, such as Eid-ul-Fitr (definitely a good holiday to catch, given the spectacular spreads they put on the tables at this time), or other religious festivals like Nowruz (another good festival to catch, since it comes with feasting and the spectacle of people jumping over the fires). There are also the typical state-wide celebrations like Independence Day, of course. The culture and festivals of Pakistan cannot be encapsulated in a brief paragraph, however, so it is best if you actually do ask locals to give you some insight into whatever celebrations may be upcoming in the area and what they signify: just remember to do it politely and show your enthusiasm to participate in or know their culture.