Minor headlines that contain more information should drop to 24 points. Subheadings, if you use them, should be 14 point and text or copy never smaller than 10 point. You can use the same ratio for any size piece you do. Use emphasis sparingly. Too often you see ads with words that are all bold , underlined , in italics , reversed or all of the above.
Overemphasizing text can reduce readability, comprehension and legibility.
When you emphasize any text, the reader's eye will be drawn to it. Another advertising faux pas is the use of all capital letters. Even in headlines, all caps are hard to read. Try using small caps, an option that uses smaller versions of capital letters. This is an example of S MALL C APS .