Make sure the heater vent (above your thighs) is open before you start. If you're driving solo make sure the passenger one is closed. You'll get some more airflow up the screen.
You only really get heat if the fan is running. Once the engine is up to temp your legs should stay fairly warm. You can help keep your hands warm by holding the steering wheel at the very bottom, the air there is warmer.
If you can handle the motion of the droplets, rain-x the screen. The wipers aren't always that good and depending on your height might not be clearing the part of the screen you're actually trying to look through.
Heat Holder flying helmet style hats are amazing, other option in bad weather is a decent crash helmet that doesn't steam up if it's wet.
As stated above, a little speed keeps you drier. There is no such thing as dry...