Search for something that is fun and involves exercise. I don't like repetitive exercises, so I would never keep doing any exercise for a longer period until I started climbing. I have fun figuring out how to climb a route and the exercise and fitness gain comes along. It probably isn't as effective at training as repetitive exercises, but it is good enough for me.
Find people to exercise with. It's much easier to agree to come along when someone else proposes it or have a regular date for exercising with a group than having to motivate yourself to get off the couch and do something on your own.
Reminded me of a comedy show routine where kids agree to play basketball and the fatter kid thought they meant ea sports
