Check that the damage is confined to the paint/primer layer itself, i.e. there is not a shallow dent beneath the paintwork damage!
Smooth out the scratched/chipped area with wet/dry abrasive paper 180 grit, finishing with 320 grit until a level surface is achieved, with a visible "contour" at least 1cm wide showing on all separate primer and paint layers.
Use a sanding block at all times to prevent ripples being visible in the finished repair. 
Dry the surface, especially bare metal, immediately with a clean cloth. Avoid touching areas to be primed or painted with bare hands to minimise future problems caused by oil, grease etc . If no further damage is evident , move on to the primer stage.
If only a small area is to be sprayed, solid and metallic colours can be blended into the surrounding panel as detailed in the Blending section.