To try this layered look, start with a button down shirt. (mine was white) Over the button down, layer a tee of your choice and over the tee, add a long cardigan.
If you want an additional layer for warmth or just to add to the "cute factor", accessorize with a pretty scarf.
One last item to mention....the shoes! I purchased J Crew's Biella patent loafers in poppy (see review here) and they are perfection. I want the black Biella's as well, but I am waiting for them to hit sale. So in the mean time, I ordered a cheap pair of black patent loafers to fill the void. I ordered them one evening from Zappos and they were delivered the very next day....how's that for service?! The style name is Beechum and they are faux patent with a synthetic sole, but they are super cheap. I paid $39.99 with free shipping; however, they are now $35.99 with free shipping. If you are in the market for some inexpensive black patent loafers, check these out. They fit tts (took my normal 7) and they are comfortable. (no rubbing, etc)
J Crew Perfect Shirt in White - Size M
J Crew Beaded Greyhound Graphic Tee (from Fall 2008) - Size S
J Crew Dream Varsity Striped Cardigan (from Fall 2009) - Size S
J Crew Matchstick Jeans - Size 27
J Crew Jersey Striped Scarf
Call It Spring Beechum Black Patent Loafers