One of the things I find surprisingly useful when engaging in world design, particularly when populating the world with notable characters is to use a set list/play list.
If I'm designing for an RPG then these lists don't usually get played in session, as I prefer an ambient soundtrack if any for actual play. They are shared with the players though to give them a sense of the mood I want to evoke.
Sometimes the set list will only be a single theme song if it's for a specific place, thing or person but it can often be a full ESP or album's worth.
For example I'm writing up a flooded urban fantasy setting where werewolves are the current focus of my attentions. This set list is currently:
The Wolf - Shooter Jennings
The Little Things Give You Away - Linkin Park
Calm Like a Bomb - RATM
Hatred is Contagious - Filter
The Warmth - Incubus
If You Fear Dying - One Day as a Lion
The Devils queen - Black Stone Cherry
By the time I'm done I expect to probably double the number of songs on the setting set list.
Individual places or people tend to have fewer songs, often only one. The song they have is not necessarily very descriptive of the place or person in its entirety but is there, like the setting set list to give me a hook into writing it.
Sometimes it might be a repeat from the setting list if it's a major component of the design. For instance The Devils Queen also features in the set list of the floating nightspot of the same name, although it's usually referred to by locals as The DQ.
The bar manager, Kenny, is always taking in lost causes despite his better judgement, his theme song is, of course, I Knew You Were Trouble by Taylor Swift.
These themes and set lists help to keep me on track when writing, especially for mood and tone and also when considering dialog in the case of people.