You can do a couple things, like closing off ways of cold air getting under your hood, like adding solid grill inserts, bumper inserts and even if you need more, you can add a belly skid/tarp or something under your engine bay, it will help a LOT.
I agree check the thermostat. You could also add a coolant heater. I have been meaning to do that for years but don't have the time. The only draw back to the coolant heater is you will have to flush the coolant more often.
Let's assume you've done the obvious, and the coolant level is where it should be.
Pick up a Prestone backflush kit ($5) and backflush the system per the directions (they are very specific so I'm not going into how).
Mine usually takes a good 8 minutes, that's with a 180* t-stat. Just a note: if you go any colder than 180, the PCM will stay in open loop as the engine will not reach acceptable operating temps.