Stiff bristle brush and vacuum. Don't even think about a wet cleanser, you'll have a cake, not a clean carpet.
Now, once that's done...
1. Wear an apron when working with flour.
2. Get a big beach towel from Wal-Mart and put it over your seat.
3. Change clothes before leaving.
If you're the pizza maker, delivery driver, etc, then 1 and 2 are your best options. Staying clean while working with flour and doing it fast, just ain't an option. You might also consider rubber floor mats instead of carpeted ones.