I'm planning to begin commuting via Bike in San Francisco - need advise!

Hi all,

My commute to work has lengthened and riding the bus is turning out to be very time-consuming. I thought it would be a good idea to begin biking because the time it takes is much shorter and it gives me the flexibility to go to the gym and make whatever stops without being concerned about the bus schedule. However, I've never really ridden a bike on the road before besides for site-seeing. Plus, I am not very fit at the moment and am hoping to improve my fitness. I am very nervous about embarrassing myself or failing. I know I should just try before I start to worry, but I was hoping you all could maybe share your initial road biking success stories or some tips and tricks?

Thank you,