Knowing your fonts.

There are four categories of fonts listed Serif, Sans Serif, Script and Decorative (Novelty).

Serif fonts have a horizontal and vertical details added to the the characters major strokes. 
It is generally considered the most legible, especially for long passages of text.  They serve
excellently in both main text and body text capacities.

Sans Serif fonts are fonts without the horizontal and vertical strokes found on serif fonts.
While this may make them seem all the same, there is a wide variety of fonts in this style. 
In small print, like on a business card, it is ideal for body text.

Script fonts are styled after handwritten or calligraphy.  Often highly stylized, they offer an
elegant choice. However, legibility is an issue, they are often smaller in size and with the
complex lettering makes it more difficult to read.  It should rarely be used for body text,
and always use a larger point size.

Decorative or novelty fonts are usually highly stylized, trendy and often go in and out of
vogue. Legibility is again a point to consider.

Modification & Legibility

Most fonts can be modified by using Bold, Italic or Underline modifiers.  Bold fonts are
heavier in weight, or thicker, while italic or oblique fonts are slanted versions of the
same font. Underlining, simply underlines the text.

You can also modify by using ALL CAPS, Upper and Lower or all lower case lettering.

The design battle comes down to legibility.  The more tolerant your audience is, the more
drastic your choices can be.

Expert advice - Modify sparingly.  These variants are like adding exclamation points or
shouting. Overuse drowns everything out.