In winter you need to make sure that there is no young growth on your lawn as this will make it more susceptible to disease. To do this gradually lower the cutting height of your mower until you are almost shaving the lawn. Do this in steps over a few weeks as you do not want to suddenly remove all the leaf tissue or cause damage to the turf.
Apply fertiliser to your lawn in the late fall. Although this will not be used during the slow growth of the winter it will be stored in the roots and be immediately available for use by the grass in the Spring as new growth begins.
Remove any debris from the lawn before the first snowfall. This includes leaves, logs, equipment, pots etc. If left in place when it snows they will smother the grass under the blanket of snow and cause damage which will make the lawn vulnerable to disease.
Before the first frost aerate the lawn to prevent thatch from increasing during the winter and to prepare the lawn for new growth in the Spring.
With care your lawn will survive the winter in good shape and be healthy and green with new growth in the Spring.