Can I do anything for my lawn this winter?

Don't fertilize or overseed till you control the weeds.

Start with broadleaf weed treatments, then get a pre-emergent.

After that, it depends on your type of grass.

I'll assume you're in the damp rainy Pacific NW, not a dry mountain area. Not really anything to do in winter, except pull weeds. Grass seed, even cool climate seed, doesn't germinate until 45F, so wait until your daytime temps are that or a little higher before overseeding. Same for fertilizing. Grass isn't really going to be growing now, so it won't use much fertlizer. Wait till maybe late February. Same goes for weeds. Hard to kill them with a chemical when they aren't growing enough to absorb it. Liming is probably a good idea too, but not right now.

You fertilize when the grass plant are actively growing or soon will be. Shorter day length and cooler temps put lawns to sleep. No clue of your climate, but think December reseeding isn't a great idea. More likely spring, maybe early spring there. Then you fertilize.

no