I would expect we could look back to both wars in Iraq, as well as Afghanistan. In the first weeks of war, the US would do nothing but push buttons from hundreds of miles away, maybe moving up the Strait of Hormuz with mine clearing operations. Iran would dig in more than anything else. Depending on the disposition of their leadership, attempting a strike against an American ally like Israel or Saudi Arabia is possible, by means of missile or clandestine operations. If the people in charge are patient enough, there would be no phase of typical land warfare. I would expect amphibious landings and parachute operations for maximum marketing power. If the conflict were to see traditional symmetric warfare, it would probably look kind of like '91, but perhaps not quite as one sided. Ultimately, American air power would put an end to it fairly quickly. Iran simply doesn't have a functioning air arm, and only has so many SAMs to launch. After this initial exchange, the US would find itself locked into a multi-decade guerilla war being fought by the same people that helped build Hezbollah. Some Iranians would probably be happy to see "liberators" if only because their appearance would suggest they would stop getting bombed and could just go on with their lives. In time American troops or commanders will completely turn even the friendly population against them, and if they don't, loyal Iranians will, and thus further facilitate an asymmetric campaign. Iranian agents abroad would probably follow some sort of doomsday protocol in the event of the collapse of Tehran. Assassinations, sabotage, and cooperation with armed groups outside of Iran.