Many things. Most of all, I'm extremely vain. I enjoy entering a room, and being one of the few people there, who is exactly at his correct weight. My wardrobe, has stayed with me for decades. I don't have to own three different 'size departments,' just in case I've put on some pounds, since I last got dressed up. Exercise, is absolutely essential to looking and feeling good. Make time for it. I work out, three times a week, sometimes more often than that. Everything, from skin tone to condition of fingernails, to strength and posture, improves via exercise.
When I was a child, I thought that movie stars looked good onscreen, because of 'chance.' Now, I know better. Sadly, too many of them smoked themselves to death, trying to stay svelte for the cameras.