The examples on this page show how to style Blogger ATOM feeds using XSLT. This example is to style it into an RSS feed but is very informative about the elements and selections for styling other (e.g. HTML) feeds as well.
Normally when you view an RSS file in a browser, you just get an XML parse-tree diagram, which is very inscrutible and un-informative to casual users. I've come up with a few ways to improve this situation. None of these affect how the RSS actually looks