Bring cash in US dollars or euro. You cannot use credit or debit cards, travellers cheques or ATMs. Repeat, bring all you’ll need in cash.
Tipping is not a big deal in Iran. In upmarket restaurants (mainly in Tehran) a 10% gratuity might be expected – on top of the 10% service charge that’s often built into the bill. But in most other places any money you leave will be a pleasant surprise. It’s normal to offer a small tip to anyone who guides you or opens a building that is normally closed. If your offer is initially refused, persist. There is no culture of ‘baksheesh’ in Iran.