Welcome iPedal! If you have been lurking for a while, you have already seen some good discussions about establishing a good aerobic base. To get started I would concentrate on frequent rides at first over duration or distance. Find a reason to get on the bike often. Do long rides as you are able to work them into your schedule and your level of fitness. Of course you will want to reach for the brass ring and go fast. Everybody does eventually.
Good to have you!