size
Contrast of size is only effective when used with discretion.
When contrasting size, be cautious that there should not be too much large type.
A rule of thumb is to make areas occupied by the contrasting element approximately equal.
Take for example; a single large letter should be followed by a word or words, which
takes up similar amount of space. The use of contrast in size is almost universal because
it is so simple, yet creates a striking effect.