Routine maintenance on your central air conditioner will help keep you cool. When is the last time you had your unit cleaned and checked?
Check your air filter. a clean filter will help your system work more efficiently.
Is your unit in the shade? If not, you may want to consider planting a tree or shrub nearby to provide shade. Keep them far enough away to allow good airflow.
If you have ceiling fans, switch them to run counterclockwise in the summer months. This will help push the cool air down.