Start now! Today! You don't have to get in touch with me right away for a full blown lifestyle makeover (that only works if you're ready to really commit), just start moving more! Park further away from the grocery store, carry your groceries to your car rather than carting them, when you can, and take the stairs- again and again. The more you move, the healthier you will become.
Get a pedometer and start keeping track of your steps. Set a goal to reach the 10,000 step mark (which is said to mean you are considered "active"). Walk with a buddy or family member, get an ipod or mp3 player and download some of your favorite tunes, or just get out there and enjoy some peace and quiet.
PS: Make sure to be safe! When walking outside, walk against traffic so you see what's coming, wear reflective clothes when you're out at night, and use the sidewalk when you can.