Make sure that you are looking for signs of pests and disease that needs to be dealt with before the next planting season. This is a good time to plan what beds need to be rotated next growing season for the best soil quality.
This is a great time to add compost from your composter or organic matter such as fallen leaves. This will break down in the soil and helps your plants thrive next year. Prune plants that need fall pruning so they are ready for the hard winter.
Add some mulch around perennials. This will give them an extra layer to help protect them from the harsh cold winter.