Sand any imperfections in the surface of the drywall, such as mud or spackle used to patch holes. The sandpaper will help create a uniform surface so no specific areas become shinier than others.
Cover the entire surface of the drywall with a stain-blocking primer, if the wall has grease, crayon or other shiny stains on it. A stain-blocking primer will prevent grease stains from soaking through the paint and causing shiny spots on the wall.
Coat drywall that does not have stains with a regular drywall primer before painting. Cover the whole wall to ensure an even base coat for paint. Use a latex-based primer to avoid an uneven finish.
Use a regular drywall primer for touch-ups. Do not use a stain-blocking primer over patched areas on drywall; only use it to cover an entire wall. Patches of spackle or patched-up drywall will look shinier than the rest of the wall if they have a stain-blocking primer when the rest of the drywall has regular primer.
Use a metal primer to cover shine from nails, staples or other metal in the drywall.