The best time to travel to Iran is during the mild temperatures of autumn (September to December) and spring (March to June). Summer is really too hot, particularly the south. And obviously winter is specially too cold, hard to enjoy the mountains and deserts. so if you travel to Iran during the summer , it’s better to visit north part of Iran like Ardabil , Tabriz , … .
and during the winter time it’s better to put Qeshm and Kish island on your itinerary.