You're really a little too far away for properly dramatic lightning.
Half the image is a black tree. Some foreground is fine for framing the storm, but IMO this is too much.
Zoom in on the interesting area! A FF 20mm is pretty dang wide for lightning. To get any sort of subject size, the bolts have to be hitting 'too close.' IMO, a 50mm would have worked better.
ASA 800 and 5.6 should be more than enough. (5.6 / 100 is my 'standard' starting recipe when shooting the small Az monsoon storms from a few miles away.) In your situation, cranking the ISO or opening the lens another stop or two would have made for a bit more punch.
50% of lightning shooting is preparation. Scout out locations near home that offer a variety of views in different directions. Then, when the storms and light are predicted to be good, you'll know just where to go for the best view. The other 50% is a willingness to 'head out' when storms are in the area. Unless you have an unusually nice view, shots taken from the driveway are usually pretty forgettable.
Gear really doesn't much matter. If you're close, it's rare to shoot wider than f/4 / ISO 100. Just about any lens will work well from f/4 to f/8. Just make sure an AF lens is really focused at infinity... Triggers are almost mandatory if you _need_ daylight lightning, but become nearly worthless once you reach sunset. The shutter and mirror delay you get with a trigger mean you usually miss the bright branching display which often occurs during the first pulse of lightning.