1. Leave the leaves, sort of.
It's true leaves are "nature's gold" as they provide nitrogen to the soil and protection for plants and wildlife. However, if leaves are not mulched first, they may mat and suffocate your lawn, and will take much longer to breakdown in your garden beds.
If you have a tree line or forested area on your property, you may rake or blow intact leaves there. However for lawns and gardens, mulch first. For lawns, run your lawnmower over leaves and just be sure you can still see grass when your done (run your rake over to distribute). For garden beds, apply up to 3 inches of mulched leaves throughout allowing any green bits to show through.
If your leaves are diseased, like tar spot often found on non-native trees like Norway maple, don't use them in your garden or lawn. It's better to bag them up and remove instead.
2. Clean up, sort of.
Again be thoughtful about what you take away from your garden beds.
Leave late summer flower stalks and seed heads up like coneflower and black-eyed Susan for 3 reasons: they provide a late season and winter food source for birds, they provide fall and winter interest to your gardens, and they will self-seed and fill out your garden with no effort. If they flop and break first, which some will, you can incorporate them into an outdoor fall or winter arrangement or bind them together to stand the group in your yard, keeping in mind where they will fall they may grow.
Hollow stalks, as found on daylilies, are perfect for hibernating insects. When blooms fade, cut the stalk leaving a foot or more of stalk to dry in place and leave. If they topple or appear too messy for your liking, put them into a loose pile in a protected spot like under a bush or against a fence and that'll do the trick.
3. Compost, sort of.
Composting discarded plant material and excess leaves is a cheap and effective way to make a natural soil amendment. However, be thoughtful about what goes in the compost bin so that you don't spread disease or seed where you don't want to.
When composting materials from the vegetable garden, keep the following OUT: diseased plants or fruit like tomato blight or blossom end rot and produce with seeds.
If adding weeds, keep the following OUT: invasive plants and seed heads like garlic mustard and dog strangling vine, any weed with a seed head. These invasive plants and seeds should be put in the garbage.
Add healthy plant material, never diseased, chopped up as much as you can to speed up break down. Remember to layer greens (including your kitchen scraps) and browns.