Lightning can be a great way to add some incredible drama to a landscape shot. This helpful video will show you how to do just that.
Coming to you from Nick Page, this great video will give you some helpful tips on incorporating lightning into your shots. Remember that most storms move from the southwest to the northeast and occur in the afternoon, meaning the sun will be in the west. They can look vastly different depending on what angle you shoot them from. If you want the dark and foreboding look, you need to be ahead of the storm (generally to the northeast). If you want a lighter, brighter look, you need to be behind the storm so the sun can light it (this helps to light vegetation and foreground elements too). Also consider a southern position if you want a dramatic mix of light. If you're a bit more weather-savvy, my favorite app is Radarscope. It offers all the common NEXRAD Level-III products and a convenient dual-pane display (with a pro subscription), which is great for keeping reflectivity and velocity on the screen simultaneously.
And of course, remember that lightning is highly dangerous and to not do anything that could increase your risk of being struck, including standing in an open field, which you might be tempted to do to get a shot. Also keep in mind that lightning is not the only hazard from storms: heavy rain, hail, high winds, and occasionally tornadoes should all be heeded. Do not put yourself at risk. I personally recommend finding a safe position, setting your camera on a tripod with a timer or remote before the storm arrives, then sitting in your car with the doors shut to shoot until it passes.