My $0.02:
Try to get out on a regular basis, every other day then build up to maybe 5 days per week. Take some days off, don't let the bike rule your life - there is more to life then riding a bike (I might get voted off the island for a comment like that here
). Start slow - there will be plenty of time to be a Lance wanna be.
If you have difficulty getting motivated to ride - remember that you will begin to feel great after the first mile or two, always remember that feeling. Don't try to go fast at first - just try to go. If you are going for fitness, set challenging but obtainable goals and celebrate when they are achieved.
The most important feature of a modern bike are the shifting components. Make sure the bike shifts well when you are applying pressure to the pedals, make sure it does not easily throw the chain. Make sure to get it adjusted after a few weeks of riding. You will most likely give up if the bike doesn't shift properly
. Also - don't worry about what bike is best, a hybrid or comfort bike is a great place to start - any moderately good one will do at first. Unless you have a physical reason for doing otherwise, start out with a main stream bike.
You don't need to spend a lot for a bike, some times a used bike is the best way to go - there are a lot of bargins. If buying new - try to buy in the late fall, shops dump great bikes for great deals at this time of year. You first bike should be considered an experiment.
Most new riders set the seat too low, thats OK until you start climbing hills, then get it adjusted properly - you won't believe how high it will go and how much better you will ride. Low seat = knee pain. If, after awhile you do get knee pain, post about it, there are lots of things to try.
Your tail bone will hurt at first, this is normal. Time in the saddle will cure that.
Try a bike club if they have a social riding group which rides 15 miles or less or get a riding buddy to help you get out.
Check in with us from time to time - share your triumphs, ask about your cycling problems and questions. No attitudes allowed here, no agendas, it's a safe place.