Limit them to humor, surprise or identification. Avoid white background. The eye takes about 30 seconds to adjust to a white background, especially if the room is dark. Type on the screen is not the same as on a page. A font that may be appropriate for print is not always legible for the screen.
Some fonts are more readable on the screen than in print.
Fonts carry emotional messages. Do not select Olde English to present the operating budget. Save whimsical fonts for party invitations. The size of the font on screens must be at least 20 to 22 point. Do not combine more than two fonts on a screen.