Like an onion
Go for multi-layering, which you can adapt to the weather and the seasons: don't dress too warmly, and remove a layer as soon as you warm up.
Protect your pants
If your bike doesn't have a chain guard, you may want to protect your pants by rolling them up or using a trouser clamp.
For your feet
Choose shoes or sandals with rigid soles. They'll be more efficient for pedaling!