I agree with Scuttle and dharma, you have to find something you really enjoy doing or you probably won't keep it up for any length of time. I belonged to a gym for a few years and thoroughly enjoyed the step aerobics classes they had, plus I actually enjoyed working out on the weight machines. It helped relieve so much stress.
A couple of years ago, my twin girls and I started horseback riding. I had ridden and had horses when I was younger and thought the girls might enjoy it. Well the three of us became really addicted to riding and a few months ago started working at the barn two nights a week for riding privileges, raking aisles, cleaning stalls, watering, etc... plus the riding we get to do. Good old physical labor and we love every minute of it!

To me it doesn't seem like the dreaded word "exercise" but it is a great work out and I am seeing a lot more toned muscles and feel so much more energetic these days. We have also been taking bike rides along the canal road near us on some of the beautiful sunshiney days we have had recently and have so much fun doing it.
To me the key is to find something, anything that is fun and keeps you moving so you don't feel it is a chore. Mowing the lawn, working out in the garden, taking a hike, swimming, playing volleyball or some other kind of sport. The people with little children, I used to put my oldest daughter on a child seat and take a long bike ride. She loved it as much as I did or when she was real small, I would put her in a Gerry and take long hikes with her, she usually fell asleep with the rhythm of my walk and the fresh air.
I had some trouble last Fall when I hit menopause and was getting really irritable and started gaining a lot of weight. It seemed the more I gained the less I wanted to move. I was totally miserable, cranky and not too great to be around at that time. I wasn't hardly exercising at all just horseback riding once a week. When I realized I wasn't doing myself any good, in fact I was creating a vicious cycle, miserable, weight gain, lethargic, etc... I decided to get my act together and I feel like a different person these days, exercise is such a mood lifter and stress reliever I realized I can't live without it. It is literally saving my mental health and my quality of life. I am so much more limber, confident and happy when I exercise. Wow, I sound like a preacher here and I think I wrote a book. As you can tell I am a little passionate on this subject because I think it is so important for us and it has helped me so much. I am a totally different person when I am exercising and feeling good about myself.
Take care everyone!
Beth