1. Tune up your bicycle.
If you can't make it into your local bike shop, do the ABC Quick Check. Make sure your chain and components are well lubed too.
Air Pressure: are you tires properly inflated?
Brakes: are they both working?
Chain and Crank: can you pedal smoothly? Are there any squeaks?
Quick releases: are they securely closed and tight?
Check: is there anything loose or rattling?
2. Wear a helmet.
If you don't own one, buy one.
3. Select the best route. Plan ahead of time using a local area trails map or check out Google's bicycling directions.
4. Dress for bicycling success!
Leave a little bit earlier, take your time, and enjoy your ride. This will keep you from sweating as much, but a little extra glow never hurt. Consider bringing a change of clothes and freshening up at work. Generally you will continue to sweat ten minutes after getting off the bike. Leave yourself 15 minutes to cool down before starting your day. Take advantage of shower facilities if they are available. Roll your clothes instead of folding them if you are taking them in a backpack or pannier. Put together a small toiletry bag of things you'll need to freshen up after your energizing commute.
5. Obey the laws of the road and be courteous to pedestrians, motorists and other bicyclists.
Have fun whisking away tension that comes from an occasional stressful workday on your bicycle commute home!