For me, what was working last year was a combination of mild dietary changes, and some exercise at the gym.
The dietary changes were to reduce needless carbs, which meant cutting out the useless snacking for the most part (with low-calorie snacks being OK, like those little 10-calorie jello snacks), and avoiding potatoes/fries and bread. Instead of pop-tarts for breakfast, I switched to a combination of raisin-bran (for the fiber) and cheerios. I made an effort to eat salads more frequently as well, and allow myself to leave some food left over more frequently. So nothing earth-shattering here.
The exercise that I was doing was to visit a local gym twice a week after work. They had these electronic bikes with an LCD screen that let you race against your own prior runs, while biking through woodlands and other virtual scenic trails. I'd do 25 to 30 minutes on the bike (attempting to always out-do my previous times per virtual lap), then spend 25 to 30 minutes using the various weight and resistance machines. The latter I don't think helped much, since if I really wanted to build strength, I think I'd have had to do a lot more of it. But my endurance improved considerably from the virtual biking.
I managed to lose about 18 pounds at my peak, in about 2 or 3 months. I've since put about 9 of them back on.
Ironically, I think I'm physically stronger now than any other time in my life, despite having the strength of a couch-potato. I was quite a weakling of a teenager, for instance. The endurance I gained while I was using the gym was very beneficial in my historical swordsmanship. I need to regain that.