I usually make notes about character back-stories or any other background I wish include and make sure to include them in the narrative when they become relevant. More attention is given to characters of my own creation than to say Sisko, Dax, or any TrekLit character. And with characters from television or stand-alone novel series featured in just one scene, I try to give a light background rather than an entire biography for those not too familiar with, for example, New Frontier. For a story currently in the handwritten stage, I just say that Mackenzie Calhoun is captain of the Excalibur and his purple eyes are a distinguishing feature of Xenexians. His first officer is Burgoyne 172, a member of the hermaphroditic Hermat species (thereby explaining the rather unusual pronouns), and so on...