Depends on the NPC caster when I DM.
Say the once druid who is now a warped evil warlock. Her misty step takes the form of dried dead leaves that slip threw craps or ride a quick breeze to her new location.
Stuff like that. I think that can really help to stick a character out for your players, and even get their minds cranking on cool personalized magic. I mean, why should Tenser, Bigsby, and Melf have all the fun?