Autumn/Fall seems to be the most difficult season to dress for. It's not quite cold enough for coats, but not warm enough to go without...and if your here in England, always be prepared with an umbrella!
My advice for this season is to work with layering thin garments.
I usually have early morning starts when the weather starts off a bit nippy and then brightens and warms up during the day. For this I don't like leaving my home in just a t-shirt or a summer top, I like to layer so I can remove layers when I want. I usually wear an open shirt as my outer wear in place of a jacket. This is a great way to feel like your covered for the chilly mornings/evenings, and still be cool in the day as my shirts are always loose and cotton.
Autumn/Fall '12 sees the comeback of the plaid/checked shirts. The high streets are full of them.