"Try to move yourself as much as possible," says Alistair Longman. "It doesn't matter if it's walking, cycling, running, weightlifting, hiking, swimming — as long as it involves some movement."
In the later half of your 30s, you start losing muscle mass, so it's especially important to exercise at this time. But remember to choose physical activities you really love, since you're less likely to continue exercising if you dislike your workouts.