Travel is associated with leaves and vacations. If you are in a mind to take a tours to Iran, then you are lucky enough that the best time to visit to Iran is RIGHT NOW.

The best time for Iran tour is mid April to October. The weather is very good and many travelers chose this span to go to Iran.
If you are lonely star, then you should plane before or after this time.

This time is the peak time of tourism in Iran, so be sure you have confirmation your stay at hotels or your Iran tours has been managed by someone.