Wait for a day in which the lawn is not soaking wet, as this makes using the aerator difficult. The Virginia Cooperative Extension advises that you should water your lawn two days before aerating it.
Place the lawn aerator at the corner of one end of your yard and turn it on. Standing behind it, slowly push the aerator along a straight line down the side of your yard, noting that the machine's tines are spinning correctly and poking holes in the lawn. Walk slowly to allow the aerator's tines to thoroughly penetrate the grass.
Aerate the entire lawn by walking back and forth in one direction as though you are cutting the grass. Turn 90 degrees and walk the aerator over the entire lawn again to ensure every section of it is thoroughly aerated.
Water the lawn and apply fertilizer once you have finished the aeration process.