No matter what genres you shoot, one of the most useful tools you'll probably comes across in Lightroom is the graduated filter. This great tutorial will show you the ins and outs of the tool as well as some neat tricks to get more mileage out of it.
Coming to you from Anthony Morganti, this helpful video will show you everything there is to know about the graduated filter. The graduated filter is so useful because it allows you to very subtly feather adjustments and effects, making it easier to make them appear natural. For example, if you want to adjust the exposure of the sky, it's often beneficial to have the effect transition a bit as it reaches the horizon; otherwise, the hard line can be a dead giveaway, particularly if the horizon itself isn't a perfect line. Furthermore, as modern sensors get better and better in terms of dynamic range and file latitude, you'll likely be performing this operation more and more as you're able to cram increasing amounts of luminosity information into a single exposure. In tandem with the radial filter, it's also a great and quick way to subtly draw attention to your subject. Give it a try.