how to nurse your soil back to health over winter

I just finished tidying my garden beds this week, replacing worn-out frost covers with new ones and cutting back my rhubarb, lovage, and other perennials that had gone a little too wild. As I'm rooting around in my beds, I can tell the soil is a bit tired. I've got weeds sneaking their way into now-empty spaces, the soil level has gone down a couple inches and I grew some BIG tomato and zucchini plants this summer, so I'm sure those beds could use a good feeding. I usually let half my garden...