The USAF should be conducting a mass bombing campaign initiated with cluster bombs and MOABs while the US Army uses heavy artillery to flatten everything. The time for nice is over, time to go full-Roman.
Raqqa should become a byword for death and never be allowed to rebuild.
Raqqa is expected to be like Mosul, in that ISIS is expected to use the same tactics in an urban environment - lots of IEDs, and very well prepared fighting positions connected by tunnels.
Raqqa is much smaller than Mosul though, and the Kurdish elements of the SDF have been proven to be very effective against ISIS (US soldiers won’t be going door to door - locals will do the close fighting).
All indications are that the US is promptly responding to any calls for fire (US Forward Observers are on hand). A dedicated Marine artillery unit (155mm) has been established within easy range - they were running about four dozen fire missions per day as the SDF was bringing the cordon in around the city.
Raqqa was getting about four air sorties per day. I think that the plan was to finish up Mosul first, and then shift additional air assets to Raqqa - but Mosul has dragged on a bit beyond schedule. If ISIS collapses, fine, but if they put up stiff resistance, additional air assets will be coming, like loitering gunships, and a lot of drones.
Lots of official statements, including from the SecDef and the CENTCOM Commanding General, have unabashedly announced a strategy of “annihilation” against ISIS - very uncharacteristic for Americans who usually use weasel words like “Defeat in Detail”. To me, it sounds like that term is intended to translate clearly into Russian, where annihilation has long been one of their theoretical principles of war.