A lawn rake is a necessary tool for anyone with a significant amount of lawn. Regularly removing thatch from the grass will not only keep the grass looking nice and green, but it will be healthier too.
When grass clippings, leaves and other lawn debris collect on the soil surface, they come together to create a spongy layer called thatch that impedes the movement of water, air and nutrients through the grass into the soil and to the roots. If this layer gets too thick, then the grass starts to brown and may eventually die.
To avoid this problem, you can regularly use a lawn rake that will slice into the thatch layer and remove some of it, making it easier for the oxygen, water, fertilizer and other nutrients to move through the dirt to where the grass roots are. A small layer (around ½ inch) of thatch is fine and even beneficial to the lawn, helping it through hot and dry conditions, but more than that should be removed.
A lawn rake looks like other rakes, but with sharper, dual-bladed tines that cut into the thatch, removing the top section. Angle the tines to be just on top of the soil and pull the rake back towards you. Use the rake in many directions over one small patch before going onto another to get the most thatch removed.
Gather all the thatch and moss that has been sliced off and dispose of it. If you leave it on the lawn, it will just become thatch again. If too much moss is your main problem, using a product designed to kill the moss before you rake it out will make it easier to get out and help you to remove more of it.
After raking your lawn, if the thatch is still very thick or accumulates quickly again, you may want to consider power raking or power dethatching. Both are harder on the lawn than using a manual lawn rake, but they will get more thatch out. After that, you should be able to manage your thatch problem on your own with regularly raking, aeration and routine lawn maintenance.