Once you arrive in Tehran and depending the time you will spend in Iran it can be a good idea to quit the turists route either to south or northwest and follow oposite direction to northeast of Iran.
Why? Trust me, you will not regret, like you will see in my next posts.
To start you can take the daily train from Tehran (departure: 5h40) to Sari (arrival: 13h55), for a sale price you can have a wonderfull train experience that is believed to be one of the most scenic train rides in Iran.
Train has been undeservingly avoided by many tourists travelling to Iran but he provides you a opportunity to mingle with locals and finally and a unic scenic experience.
If you will decide to follow my sugestion, not forget to buy your ticket (2nd class train w/ seats) the day before and make your best for not to loose your train to the lush green Sari.
Enjoy your ride!