Ridding your lawn of moss typically requires a two-pronged attack! Firstly, you want to remove the moss then try to stop it coming back. The best way is scarifying, physically removing the moss by raking or a mechanical scarifier (for larger areas) and then reseeding grass to stop moss regrowth. Moss in a lawn usually means there is a problem:
-Poor drainage
-Too much shade
-Acidic soil
-Lack of fertiliser
-Grass cut too short
-Heavy foot traffic
Depending of the seriousness of your moss problem, in mild cases you may just need some simple scarifying and then improvement of the overall health of your lawn with fertilizer (some fertilsers can also contain moss killer for double effect). If the problem is more serious you will need a combination of moss killer, scarifying and reseeding grass.
The best time of the year to try to get rid of moss and improve the health of your lawn is during the spring and autumn months. The best time to seed grass is late March to mid-October.