When ever I design templates I always try to ensure that all of my HTML elements are styled properly. It's very easy to forget element and to see how they look. I've tried to create a test file with all the code you will need to be concerned about on a basic level. You will find that every template and every CMS may introduce new specific styles you need to be aware of, but from a basic perspective this should cover them all. Let me know if you find more that need to be added and I'll make the proper revisions. I am far from perfect and I'm sure could improve my process.
I recently was looking for a good way to display HTML code in my content and looked at quite a few options. I never use the pre element but that is what was recommended. The problem with using the pre element is that it will process the html and won't display it so for every < and > you end up having to put in the ascii html code for it to get it printing.