Help animating sword

My spriting skills are very basic and I ran into a bottleneck when I attempted to animate a simple knight to swing his sword.  I ended up with his sword just moving up and down instead of down and across his body, like swinging a bat. I can picture how it would look in my head but have difficulties when it comes to transferring that to the canvas. If someone could suggest on how to approach it or show me or really just how to improve my sprite I would appreciate it.