Doing 30miles 5 days a week can be very strenuous on your body, I would recommend aiming for 2-3 days a week. See how your legs go getting used to it. Once you feel comfortable you can start doing more days. Start small and aim big.
Be sure to carry enough liquids with you and make sure you are on some kind of vitamin and mineral supplement along with a healthy diet to help your body cope. It might also be a good idea to carry some food (such as a mars bar) to give you suger energy incase you get tired.
Like any exercise, you will get tired, so just be prepared for it.
Make sure your bike is set up correctly, speak to your local bike shop as a misfit bike could result in an injury.
I could also recommend investing in bike shorts, gloves. Helmet is essential! Also clip-less peddles and proper bicycle shoes will make a big difference in peddling efficiency.
Last but not least, plan your journey carefully as cycling on the roads can be dangerous, try and stick to bicycle lanes and quiet roads.
From a personal experience, I started cycling to work (10miles each way), I was very unfit at the time but still healthy. At first it was very tiring and my legs were taking strain but after a couple of weeks I got used to it. Now its part of my daily commute and I kill two birds with one stone, exercise and getting to work.
