It depends on the situation.
In VMC if fire not out: I would tell the PM to continue to work the appropriate ECAM/QRH as appropriate. I would turn downwind manage speed appropriately to set up for the fastest (stable) circuit possible. As the airplane is doing that I would change the destination (time permitting) throw in the approach into MCDU for reference on final, activate the approach, time permitting make a quick PA, manage speed appropriately to set up for a 2 mile final or so, abeam the threshold AP/FD off and set up for a tight base to final, planning flap full, MED auto brake and full reverse. Come to a stop and set the park brake. If fire is still going on with secondary confirmation (ATC/Fire Truck/out window etc) I would go into the checklist - pax evac.
In IMC essentially the same thing. As PF I would fly the airplane and set myself up for a successful approach. Ask to get vectored onto the approach at the lowest (closest) altitude possible from ATC. I would fly the airplane and navigate it while having PM take care of the extra bit. Otherwise similar to the VMC.
Whenever I fly I generally always think about this situation. I would always brief (even though not required by SOP) which runway is our best option in the event of a quick return (fire type scenario).. Basically discussing the longest into wind/open runway (may have other factors like the approach available etc). Anything else you have time to climb up to a safe altitude and decide what you're going to do.
Another technique that I use, when it's actually IMC/clouds below MSA if I do not need the SEC flight plan for an engine failure procedure or something else I will plug in the routing only for the emergency return I would like. That was if need by the inbound section is all ready to go to help me navigate to it.