If moss is a problem on your lawn you will need to scarify it out. You may also consider applying a weed and moss-killer product before scarifying. This will help to kill and remove more of the moss. Allow the moss to turn brown/black before scarifying.
It is important not to scarify too early in spring, the grass should be growing fairly well to avoid gaps being filled with unwanted weeds or weed-grasses. Scarification is best combined with other operations, like topdressing, overseeding and applying fertiliser. Where other work is planned, scarification should be completed first.
If the resulting sward is very open (perhaps if there was more moss than grass), over-sowing with a quality grass seed after scarification will help to improve the sward. If you do over-seed, choose grasses that suit your lawn (fine grasses for ornamental lawns (non-ryegrass mixtures) and wear tolerant grasses for utility lawns (with ryegrass mixtures).
Moss is more of a problem on shady damp lawns and the best control is to address these problems. Damp lawns should be regularly aerated and top-dressed to increase drainage potential. Shade from trees and shrubs may be relieved through sensitive pruning, however, this may not always be possible. In such cases make sure that you do not cut the grass too closely, but continue to cut it regularly. We would suggest that a cutting height no lower than 1 inch (25 mm) would be appropriate.