When I first joined LibraryThing, one of the things that frustrated me about tagging was their use of the comma as a delimiter in the tags field. That meant that anytime I entered a subject heading that included a comma, I ended up with not one heading, but two. That means my entry of "Monroe County, Mississippi" had the tags "Monroe County" and "Mississippi", but not my desired combined tag. You can still use those two tags and search for the tag mash of the two terms, but the searches take longer. I learned a trick from fellow genealogist Jeff Haines. He was using a two letter abbreviation for the state followed by a colon and then the county name. In other words, I could enter "ms:monroe" or "MS:Monroe" (for those of you who want to preserve capitalization) as my tag. I had my tag mash ready made so that searching didn't take as long, and it shortened the entire phrase. I liked this manner of entering my genealogical resources that were specific to one county.
Another thing I learned from Jeff's tagging was that he was tagging family names in a similar manner. Instead of using "Perkins family", he used "family:Perkins". I actually often use both tags now. Why? I am so accustomed to the official Library of Congress Subject Headings format for names, that I tend to use it automatically, but there is an advantage to the other form. If I look at a list of tags, I can quickly see all of the works I have on various families all in one place.
Librarians have know for years the value of using "controlled vocabulary" to help locate things. That's why we have that options in our catalogs through our subject headings. It's important that you consistently tag things the same way so that you know how to search for the item. Every now and then, it pays to go take a look at your tags. You may find things that you need to change. You may have accidentally misspelled something. You may have entered it as "periodicals" most of the time. However, leaving off the "s" just once may make something unfindable for you. You can correct these little problems as you see them.
Tagging is a very personal thing. Find something that works for you. Just be consistent!