Aerating is best done in the spring and fall. Aeration opens the soil and allows air penetration and better water movement in the soil. This makes water and nutrients you give your lawn more available to the grass. It also stimulates root growth and development. In the fall September and October are good times to aerate.
The best results for aerating will be on a moist lawn. If your lawn is dry water it before you aerate. There is no need to pick up the plugs that result from aerating. After a couple of rain showers or some watering they will disappear.