Above all, a traveller to Iran should take outfits which respect the rules of decorum in the Islamic Republic, compulsory for everyone, including tourists, and especially women.Women should take a scarf with them to cover their hair (in winter, a hat can flatteringly replace the scarf), as well as loose clothing which covers the shape of the body and long sleeves . Several friends who had travelled to Iran from India took Indian-style tunics with them, with wide trousers, which were very practical for travelling in summer. Iranian regulations also stipulate a certain type of clothing for men (short sleeves are tolerated, but shorts and other Bermuda shorts are prohibited). If you're unsure of which clothing to take, just take one outfit for getting off the plane, then head to the bazaars and other shopping centres to be inspired and stock up on site.
If you are lucky enough to be invited for a meal in an Iranian home, think of taking a smarter outfit.
Don't forget to take a camera or a video camera to immortalise the scenery, palaces and other historic monuments you'll come across on your travels, as well as a small travel dictionary which will allow you to communicate more easily with the Iranians.
On the health and safety side of things, it could be practical to take acopy of your passport with you and to make a copy of the page where your visa is stamped, which is always useful if you lose your passport. Medicines are widely available in the pharmacies, and they're generally of a high quality, but you'll be glad you took your anti-diarrheal medication with you on long bus or train trips.
Finally, have cash with you (euros or American dollars), since western bank cards don't work in Iran.