Structure 

The underlying structure of a typeface includes all its characteristics, plus things like the basic shape of the characters and their spacing. Creating contrast with the structure of fonts is an established method of combining fonts. But it’s a good idea to pick fonts that have at least some structural elements in common (such as x-height or the weight of the “normal” style) rather than those that are wildly different. 

Mood 

Mood is one of the more subjective areas of typography. It refers to how formal or informal a typeface is, as well as whether it’s playful, feminine, masculine, casual, serious, etc. 

For example, Comic Sans is an extremely informal font that’s inappropriate for use in most situations. Bickham Script, on the other hand, is very formal but gives the wrong impression for things like business correspondence. 

When combining fonts, it’s important to find typefaces with similar moods. Combining a playful font with a very serious one is going to be jarring to the eye. 

Decoration, Color, and Texture 

These things aren’t inherent characteristics of typefaces, but they are useful when combining fonts. Unifying (or creating more contrast) through color, decoration (such as underlining), and texture can be a very effective technique.  It can be used in flyer printing to attract people's attention.

Conclusion 

Effective font combinations are a hallmark of good design. Designers must master this skill if they want to create exceptional designs that set them apart from their contemporaries. 

Consider the guidelines included here as jumping-off points to explore how to combine type effectively. A solid foundation allows for more efficient experimentation, without spending hours on completely unsuitable combinations.

From here, designers can practice creating their own style and methods for effectively combining fonts, deviating from the guidelines as necessary with more confidence that their final product will be a delight to users.