Rails is more about making web applications that actually do things than it is about making web sites that just look nice.
But sooner or later, some attention needs to be given to one's appearance.
Enter Bootstrap.
At its simplest, this provides a CSS file to stick in the Rails project, which makes it easy to turn a site that looks boring into a site that still looks just as boring, but with the crucial difference that it now looks like a boring site from 2013, rather than a boring site from 1993. And that's exactly what I've done.
To be more specific, I copied the bootstrap.min.css file into the stylesheets folder, commented out most of the default Rails CSS file, and used the Bootstrap Starter Template to get me going.