As Authum is approaching, what can I do to prevent weeds in beds.

You can put a coat of preen over the area before winter comes. Add mulch also

As you take up the annuals and trim back the perennials, pull all the weeds you can. I then put down Preen Weed Preventer. It will keep weed seeds from germinating.

put down any fertilizer you want, like manure, and then MULCH

The goal of putting mulch is to reduce your work load in pulling out weeds. However, weeds will still sooner( not later) continue to poke through. So go the extra step and put down landscaping fabric before you spread the mulch. It is a one-time expense, and will greatly reduce your maintenace.

If you get snow where you are, wait until the snow is melted before you do this yardwork. That way you don't risk losing mulch with the snowmelt runoff, and can cut the landscaping fabric around the new plants shooting up.

Like the previous lady mulch is good but it will not totally kill the weeds much of the weeds will be dying back now short of using chemicals the mulch is your best option Good luck