Sounds like you are on the right track. Mark out your future garden, dig up all the grass, then if you can, do something called double-digging. Here is a link describing what you ideally should do:
http://www.rhs.org.uk/advice/profile...le_digging.asp
For garden beds, this is a really great idea.
For the rest of your stuff, alot of people trim back all perennials once late fall hits. Others, like me in a Northern climate, leave the seed heads in place for the birds to eat over the winter. I do a spring cleaning instead of a fall cleaning.
If you clean out your beds, what you do is wait until late fall, then cut all the perennial flowers and plants down to the ground and remove them. You can, at this time, put a layer of mulch over the top and wait for winter. In the spring, plant as usual.
Hope this helps!!!