Landscape photography often takes at least a bit of editing to produce a completed image, and as such, you will usually be doing some kind of editing work on the sky. Lightroom's newest version has a wide range of useful tools for doing this, and this excellent video tutorial will show you some of the options for selecting and adjusting a sky and the pros and cons of each.
Coming to you from Matt Kloskowski, this great video tutorial will run you through using the Select Sky and Graduated Filter adjustment tools for editing a sky in Lightroom. Graduated filters used to be the tool of choice for this, and they still work quite well if you have a relatively flat horizon. On the other hand, if your horizon is rather uneven due to things like trees or mountains, it might not work as well, which is when you should consider things like the Select Sky function. The beauty of Lightroom's new masking tools is that you can use them in tandem with one another, such as a graduated filter intersected with a luminance mask, allowing you to be both precise and efficient. Check out the video above for the full rundown from Kloskowski.