A lawn is a vital parts of most gardens providing somewhere to play and relax. The more you use your lawn the more likely it is that compaction will give you problems with drainage which will spoil the look of the grass.
Where water is sitting on the surface of the lawn drive a fork down into the soil to the full depth of the tines over the entire area.
Rocking the fork backwards and forwards as you work will open up holes down into the soil to speed up drainage.
In severe cases you can rock backwards on the fork to lift the surface and create large air pockets underneath for drainage.
Work from the far side of the lawn using a board if necessary to spread the weight and save causing any further damage.