Bumpy lawns happen no matter how prepared you are. Even if you spend a lot of time and effort to level out your yard before you install a lawn, both foot traffic and rain run-off wear the soil and affect the shape of the land over time, turning once-pristine ground into a battered landscape pock-mocked with divots, depressions and holes. Fortunately, you can fight back against the effects of erosion using a technique known as topdressing. Adding a mixture of top soil and sand to lower areas levels out the yard and makes it foot traffic friendly once more.
Pour equal amounts of sand and top soil into a wheelbarrow. Mix the two materials thoroughly with your hands or a shovel.
Shovel the mixture of top soil and sand into the holes and depressions in your yard. Fill grass-free areas with the mixture until the new top soil is level with the surrounding high spots, but only add up to 1/2 inch of the top soil mixture if the yard's covered in grass -- adding more can kill the lawn.
Rake the added top soil smooth to level it out. Add more top soil to level out any remaining depressions revealed by the raking. Be aware that holes deeper than ½ inch in grass-covered yards will remain even after raking -- do not add extra top soil to these depressions yet.
Repeat the process in six to 12 months to finish filling in the holes in grassy yards. Add up to 1/2 inch more of the sand and soil mixture to the yard during the second levelling. Continue adding up to 1/2 inch of the sand and soil mixture every six to 12 months until the lawn levels out.