Visit Google's how-to guide on creating Custom Dimensions.
Be sure to set the 'Scope' to 'Session' for any Custom Dimensions receiving Demandbase attributes.
The Custom Dimensions are correlated to Demandbase attributes by index, NOT by variable name. Be sure to create the Custom Dimensions with the same indexes as found in your Demandbase Google Analytics Connector mapping. If you make a mistake, simply rename the Custom Dimension or rearrange the Demandbase mapping.