Depends on what is to be painted.
suspension , rear end housing, bottom of car ect. degreaser & scrub , then pressure soap and water , repeat if needed.
body steel after blasting, dawn dish soap and hot water, every inch of car, cowl, inside doors, hinges, qt window wells, and pillars 3X if soda blasted. Then wipe & blow dry and seal with epoxy.
Primer on car just use PPG 330 grease and wax remover, wipe on with soaked new rag and follow with dry new rags allow time for evap before tac or sealer.
If you soap and water the primer you need 3 dry days to get it out of the primer.