There has been a lot of good advice posted already, and maybe what I am going to say has already been said. If so pardon me.
Develop a love for an activity and let it become a lifestyle. Don't pick an activity because it is great for a specific fitness or weight loss goal and then force yourself to do it. Try things,whatever they may be cycling,hiking, jogging, swimming, team sports, etc. etc. until you find your love; then you will eagerly make time for that activity,. This will yield fitness, weight and psychological benefits. Nothing is worse than doing an exercise that you dislike because it burns more calories an hour than one that you do like.