Whether you drive, bike, bus or walk to your new job, it's smart to test drive the route before that first important day [source: Huhman]. Google Maps doesn't have a "rush hour" button that will automatically double the time of your daily commute. Plus, traffic is a lousy excuse for being late, since the rest of the office had to battle the same gridlock but still managed to make it in before 9:37. If you take public transportation, have your train/bus arrival and departure times, as well as any transfers you need to make, down pat well before your first day. Do you have to drive to the train or bus station? Master that route as well. Have a back-up plan handy, just in case.
Once you know exactly how long it takes from your door to your desk during rush hour, tack on an extra 10 minutes for good measure. It never hurts to be early for your first day.