I started commuting 3 weeks ago; 21 miles roundtrip. I'm not in shape so I take baby steps, I don't ride every day. My objective is twice a week at least; more if I feel like doing it. I actually ride on the weekends and some evenings with my girlfriend too which I want to keep doing more! :-)

What helped: gatorade. Drink while you ride. When you arrive, eat as soon as possible and don't let the hungry feeling last, eat. Coffee will dehydrate you, it's not a good idea. I'm a coffee lover (read: roast my own beans, grind etc) but I don't drink any when I commute ;-)