I would start prepping the bed now, amend the soil, and then either mulch it well or plant a cover crop. There are various ways to do this.

The traditional way, and frankly, what I would probably do, would be to pull the weeds (don't forget to use them to start a compost pile or bin!), then turn over or till the soil. I would work in lots of compost or other organic matter. I would then mulch deeply or plant a cover crop, so that you don't just grow loads more weeds by Spring. If you plant a cover crop, plan to turn or till it under in Spring. If you mulch, you can just rake it back to plant.

Another way to approach it, especially since you have so much lead time, would be the "lasagna gardening" approach -- lay down cardboard or several layers of newspaper to smother the weeds, then pile organic matter on top. You can learn more about this approach in the Soil, Compost, and Mulch forum.

It's a great idea to start this fall, makes spring planting a lot easier, and less stressful!

There is a lot of great info from previous threads on this forum. Below is a link to a discussion a few weeks ago with a lot of great ideas on starting a new garden.

Good luck!

Here is a link that might be useful: starting a garden