Verisimilitude

Verisimilitude is something you may want in your games. Maybe, I don't know you.

It can be done following these two steps:

1) Come up with a bunch of cool names

2) Connect them in a diagram, and then figure out what those connections mean

... And you're done!

Internal coherence (which forms the basis for everything else) is given by  the presence of details (the cool nouns you made up earlier), existence of connections between them (ditto), and persistence of those details throughout time (you may want to record them somewhere)