Fall feedings: If you only fertilize your lawn once a year, autumn is the best time to do it. In fact, your lawn would appreciate a light application of fertilizer in early fall and again in late fall.
Aerate: If you didn't aerate in spring and your lawn needs it, fall is a great time. Don't overlook the importance of aerating. It'll help your lawn thrive.
Continue mowing: As temperatures cool, your lawn will grow faster again. Keep mowing regularly through the end of the season.
Fall cleanup: Clean up fallen leaves. If you don't want to spend time raking them, run your lawn mower over your lawn two or three times. This will chop the leaves into fine pieces; they quickly decompose and add to your soil's structure. Or rake up and compost the fallen leaves.
Overseed your lawn: Most Pacific Northwest lawns will have cool-season grasses, so autumn the best time to overseed or grow a new lawn from scratch. Plan carefully; your new grass needs at least a month before your first average first frost so it can get established.
Attack perennial weeds: Most perennial lawn weeds, such as dandelions and ground ivy, are most susceptible to attack in fall. Treat them with a broadleaf herbicide (there are chemical and organic choices available) or pull them by hand.