I was chatting with a customer this afternoon who was having trouble setting the default font on his XtraRichEdit. Sure, changing it at runtime using the Font drop down on the Ribbon bar works completely fabulously ;) but he wanted his users to start just typing away in Century Gothic.
Easy peasy, says I: we have a property for that.

This is also accomplishable via code:
richEditControl1.Document.DefaultCharacterProperties.FontSize = 12;
richEditControl1.Document.DefaultCharacterProperties.FontName = "Century Gothic";
For more information, check out the documentation.
Hope this helps!