Winterizing your raised beds is fairly Simple.
The bed should be cleaned out of weeds and dead plant material.

If the soil is low add additional as necessary.  You can also wait and add in the spring before planting.

Finally, add a layer of mulch or compost. An alternative is to plant a cover crop.  November is a little cold, but for next year, consider planting cereal rye, winter wheat, winter oats, fava beans or phacelia between Sept. 15 and Oct. 15. Cover crops inhibit weeds, stave off erosion and can be worked into the soil as organic matter in the spring.

If the bed needs structural repairs this would be an opportune time to do it.

Physically protecting the beds in winter is usually not necessary, but you might consider covering it to protect from damage if you feel it is necessary.