Air is the medium that carries energy from house during the summer to keep the temperature cool. As the air goes through the intakes and past the air conditioner's evaporator part of the energy is removed. The air then travels back to the living areas of the house to absorb more energy. One major factor that affects the energy efficiency of this process is the flow of air.
The most obvious topic here is the air filter, but that aspect has already been discussed plenty so we'll look at other points today. First, check all vent ports to see if any objects are creating blockage. Move any objects covering the vents away to where there is at least a foot of separation. Next, check the flexible duct work in the attic to see if there are any kinks. Straighten out the kink and to prevent air flow restriction.This is only relevant for flexible ducts. For sheet metal ducts check for air leaks. It is an easy test that only involves placing your hand close to any connections to feel for air flow. Seal up any suspect areas with mastic sealant or metal tape.
Using this checklist should help to tighten up the efficiency for your home's central air system. These tasks are all very simple and low cost making them well worth the time and effort.