Fall is a great time to fertilize your lawn, especially cool season grasses like Bluegrass and Tall Fescue. By fertilizing in the fall you're building up the root system but because it's cool the top won't grow as well so you won't need to mow as much. Before spreading your fertilizer you want to top dress with compost. Compost is a great additive for the lawn, especially if you sprinkle a quarter to a half inch layer on top of the lawn. It will work its way down and when down there will feed the root system and help with soil/water drainage and retain some moisture. After the compost, get some granular fertilizer, whether chemical or organic, but get a fertilizer that's lower in nitrogen and higher in phosphorus and potassium so it feeds the roots. Sprinkle it around per the instructions and your lawn will get through the winter better and start up sooner in the spring.