The history of tea culture in Iran started at the end of the 15th century. Before that coffee was the main beverage in Iran. However, most of the coffee producing countries were located far from Iran, making shipping very difficult. With a major tea producing country, China, located on a nearby trading path, "the silk road", and the shipping of tea was much easier. That was a main reason why tea became much popular in Iran. As a result, the demand for tea grew, and more tea needed to be imported to match Iran's consumption.
Iran failed in their first attempt to cultivate tea in their own country in 1882 with seeds from India. In 1899 Prince Mohammad Mirza known as "Kashef Al Saltaneh" who was born in Lahijan, imported Indian tea and started its cultivation in Lahijan. Kashef, who was the first mayor of Tehran and an Iranian ambassador to India under British rule, knew that the British would not allow him to learn about the secrets of tea production, as it was their biggest business in India at the time. So being fluent in French, the prince pretended to be a French laborer and started to work in the tea plantations and factories to learn how to produce tea. Ultimately his plan was to take back some samples of this tea to Iran to cultivate. He was successful in this endeavor only because of his diplomatic immunity which stopped the British from searching his secretly stashed sample. At the time, Kashef brought 3000 saplings into his country from the Northern part of India, Kangra. He started the cultivation in the region Gilan, south of the Caspian Sea. The climate there was well suited for tea cultivation, and the tea industry quickly expanded in Gilan and Mazanderan region. Kashef’s mausoleum in Lahijan is now part of the "Iran's National Tea Museum".

Generally beverages are not served with meals in Iran, aside perhaps from a glass of ice water or dugh. Nonetheless, Iranians are great tea drinkers. Chai is the national beverage – some would even say the national pastime. It’s served at the office, in mosques and bazaars. Along with the hammam (bath house), the chai-khaneh or tea house is a fixture from one end of the country to the other. Tea plays a social role and ends every meal, at which time everyone returns to the living room. The tea leaves infuse in the tea maker, set atop a samovar. The hostess pours a little of this dark liquid into a glass and brings it up to the light to assess its color and strength. Then you pour the very strong tea into small glasses. Then you dilutes it with boiling water from the samovar to the taste of each guest.
-> never use a tea bag, which often contains tea “dust” rather than full-flavored leaves;

The basic principles:
- The water must fully boil, but never the tea;
- Always rinse the tea pot with hot water before filling it with boiling water;
- Place a sufficient quantity of tea leaves in the tea pot even if it means having to dilute the tea in the cup with boiling water
If you don’t have a samovar, take a kettle with a wide open top; remove the lid; reduce the heat under the kettle once the water has boiled and place the teapot on top so that the heat is retained but the flavor is not destroyed

en.wikipedia.org/wiki/Lahijan