Introduction

Words are communication. What do they say? The meaning should come before the look of the type is considered.
Remember: The primary task of graphic design is to create a strong, consistent visual hierarchy, where important elements are emphasized, and content is organized logically and predictably.
Therefore, choose typographic styles and sizes that are appropriate to the meaning and will serve the text's relative importance in the hierarchy.

From the top down: places in the hierarchy

Headlines: Stop 'em and grab 'em, fast. Headlines work best when they're both visually and verbally interesting. The largest type on the page, heads should always stand out from subheads and body copy., although they don't have to be located at the top.
Subheads: Hook'em into reading more, by expanding and explaining the basic idea of the headline. Distinguish from heads and copy.
Body text: Make sure it's both legible and inviting.
Captions: Connect readers to pictures and story. Often a bit larger than body text. Be consistent.
Pullquotes and other breakouts: Add interest. Be creative.
Design with these relative positions in mind, exploiting all the variations used for emphasis and legibility.