On the elliptical machine, should I focus on speed, incline or resistance?

The short answer is all three. When it comes to burning calories, you want to activate as many muscle groups as possible, while keeping your heart rate elevated. Adding resistance and incline on the elliptical does that. But you also can’t move too slowly because your heart rate will slow down. Don’t think about it too hard: Aim to scale as high as you can, as fast as you can, with as much resistance as possible, for as long as you can.