Choose an activity you enjoy and exercise becomes easy. Seems like sage advice.
But what if my chosen activity is sitting on the couch...? Or driving fast...? Or eating...? Or reading...?
For most of my life I have been active. Basketball, volleyball, tennis, occasional running, a lot of walking... Recently, though, working full time and raising four children reduces my personal time to the point where I often don't feel like doing anything active. I would rather drive fast, eat, read or sit on the couch.
To shake myself out of that slump, I have started swimming. Not a lot...maybe once every week or so. I swam a lot as a kid and used to lifeguard. For me, swimming in a warm pool is a fabulous feeling and I thoroughly and completely enjoy it. It has helped me become a little more active recently.