An issue comes up every now and again with some of the folks I work with around the use of hierarchy in typography. Of course, there are differing opinions out there around the use of different styles of a typeface in a document, but I am of the school of thought that advocates hierarchy. This can sometimes also create anarchy.
I referred to Ilene Strizver, one of the gurus of typography, for her take on this. In one of her articles which I've saved (I save a lot of articles) she talks about the effective use of typographical hierarchy. Correctly and consistently used, hierarchy can make a text-heavy piece read better and also make the important portions of the document stand out. A document doesn't necessarily have to be text-heavy either for this to be effective. (Below is an example of a typical, text-heavy document we all are familiar with.)
Once you've used your grids and guides and know the overall color of the piece, it's good to select a typeface that has a lot of weights and is legible for what your project is. It is OK to use a contrasting typeface to differentiate bewteen headlines, subheads, and body copy. But, try to keep it to only two different faces - like a serif and a sans serif.
You can vary the point size of the type in your document, but make sure that the reader can tell that you're using this tactic. If you're going to use it, make sure it's obvious.
You can also use all caps at times. Ilene says, and I agree, that a little is good, but too much is too much. All caps in more than a few words get really hard to read. Italics are good, too. Just make sure they're the italic version of the typeface, and NOT the italicize function in your page layout program (why is that option there, anyway?). This goes for bold type as well.
Lastly, use small caps, if your chosen typeface comes with them. They're great to use when you're trying to emphasize a portion of text and don't want to use another type family. Again, the "caps lock" key is not small caps, so don't do that.
Here is Ilene's graphical representation of these tips from her article.
Hierarchy in type can not only look good and professional, it can also be fun! I love to sit for hours and hours playing with my typefaces - I have no life, remember. A few simple tricks of the trade can help your document, brochure, postcard, or business card move up a notch in the typographical sense. (Let's hope my colleagues read this and get the hint...)