Keep After Slugs
Don't turn a blind eye toward slugs because they are still laying eggs for next year. Use traps, diatomaceous earth, or whatever method works, just keep them from multiplying. If slugs are a big problem, consider raking leaves off your garden beds and leaving them bare for the winter so the cold will kill any exposed adults and eggs.
Cut Flowering Weeds
Weeds are shedding their seeds far and wide so if you've gotten behind in your weeding, cut those with flowers and seed heads first. Cut them gently to avoid scattering the seed, and drop them into a plastic or paper bag and dispose of them. Don't add them to the compost pile unless your pile gets hot enough to kill the seeds.
Adjust Soil pH
If you need to raise or lower the pH of your soil, add the required amendments, such as sulfur or lime, this fall because they take some time to work. Take soil samples from different parts of your yard and garden and test them separately so you can apply what's needed for each particular use.
Water Newly Planted Perennials
Plants that are still developing new root systems need ample water in the fall before they go dormant. Roots grow until the soil temperature gets down to the low 40s, so moisten the entire root zone once a week unless you have a soaking rain.
Move Houseplants Back Inside
Gradually condition indoor plants that have spent the summer outdoors to lower light conditions. Move them to a shady spot outdoors for a week, then move them into the sunniest spot indoors for a couple of weeks before moving them to their permanent locations. Dunk them in soapy water to clean the foliage (a sink or bathtub is handy for this), and spray with insecticidal soap if insects are a problem.