I’ve been sheet composting since before I knew what that meant. Basically it’s just composting right in your beds, which at this time of year means sweeping up all the dropped leaves from the trees and raking them around the base of the plants. Sometimes there are apples in there, or cones, or whole plants that were pulled out.
The only rules are no diseased foliage (so I never use rose foliage or branches) and no weeds. Many weeds can set seed even after they were pulled out of the ground; better to just toss those or compost them in the traditional way.
You can compost kitchen scraps this way as well, but I usually bury those slightly for aesthetic reasons.
Yesterday I put the leaves from the purple ornamental plum around some newly transplanted Euphorbia. Their blue foliage with the burgundy and yellow leaves underneath looks great, and I avoided spending $100 on mulch for the beds. Come spring, the soil will be loamy and shot through with mycelium from the fungi doing their work. The plants will have had relatively warm feet all winter, so losses are less than if they were uncovered.
The key to keeping your garden attractive while sheet composting is to keep your edges clean and sharp and keep the compost in place. You can turn the soil a bit to hold lightweight leaves, or keep all the material raked in the beds until it starts to break down and form a mat over the soil. That takes about 2 weeks with a little rainfall (or the hose).
All winter long, as I pick up debris around the yard, I toss it into the beds. Smaller pieces break down faster, and the plants won’t be vying for nitrogen because they’re mostly dormant.
In the city I didn’t have room for a compost bin, and that’s how I came to sheet composting. I have room now, but I really like the way the beds look with the seasonal detritus used as mulch. At the LA Arboretum there’s an enormous Ginkgo that sheds seemingly acres of bright yellow leaves. It would be a travesty to pick them up, they’re lovely spread over the blue Senecio and herbs around the tree.