Even with levels on tripods, visual displays on cameras, and optical perception, getting your image aligned how you want both horizontally and vertically may sometimes take some post-production adjustment. Here is a more effective way to do just that.
Rather than doing the cropping and rotary movements simply with the crop tool, the Transform panel is a smarter way to handle such edits. Even if you do want to crop your image to a different aspect ratio or to eliminate certain things from the image, there are much more refined controls for adjusting the image size, alignment, and rotation than the rudimentary controls of the crop tool. Like most other tools in Lightroom, the Transform panel has some incredibly helpful controls for harnessing more control over your edit.
For those of you who want to use less time, the panel has some fairly intuitive options for automated adjustments to alignment and perspective corrections. If you're like me and you are a bit pickier with the adjustments, then the manual controls are simply perfect for adjusting for those things that were either missed or out of your hands out in the field. Even though I level out my tripod for each shot, sometimes, I just don't get it quite right and my horizon line is still slightly slanted. I have found the transform control to be a much more effective way of correcting image alignment, basic cropping, and applying needed perspective corrections.