Use google maps and a select the bike option to map a route to your office. Chances are your city has a big enough network of bike lanes to minimize the time you have to spend riding on a busy road. Do a practice run on the weekend not only to familiarize yourself with riding on the road but also to get a feel of how long it will take; I find that google maps tends to underestimate the time by about 5 minutes.

Also if you haven't ridden a bike in a while I suggest riding around your local park loop first to build up some bike handling skills; being able to ride a bike in traffic is a different skill from just being able to ride a bike. You need to be confident riding with one hand in a straight line (you need to use the other hand to make turn signals) and be comfortable looking behind you without making the bike swerve in the direction you're looking.