Dress normally - If your ride is less than 30 minutes (7.5km), the chances are you can just ride in your normal work clothes. Unless you want to ride fast, you can just cruise into work on your bike - no sweat!
Find the best route - Don't just take the route you would if you were in a car, try looking for routes along bicycle paths or back roads, this will ensure a smooth and enjoyable start and end to your working day, it sure beats the stress of being stuck in traffic!
Mud guards - I guess they're called that for a reason - they can protect your work clothes from dirt and rain that might get sprayed up from your wheels.
Use a pannier - Make use of the bike to carry your belongings rather than a rucksack, freeing up your back will make you more agile and you'll feel great.
Carrying your work clothes? Roll rather than fold them and avoid creases.
Keep your cool - Learn to keep calm and not to react to angry or impatient drivers, keeping a cool head will maximise your safety and make the commute less stressful and much more fun!
Ride with confidence - Don't worry about holding up other traffic. Being more visible and taking a primary position is the best way to stay safe. Only let people past when you feel safe.