What is proving very fun for my players is linking prominent NPCs from the module to their backstory. During their background creation I tried to steer important characters to be existing NPCs, so I knew they'd come up. I'm also switching out npcs in the module to NPCs the players themselves came up with in the module. My players' did not take a liking to Thames Grimsley at all, so now an in-game uncle became the defacto face of the dockers, who the party has a much stronger connection to.
Other examples are one of the players being the (disliked) son of Benedict Pemberton, who doesn't know his father is secretly dragon. One player has the lady of the forked tongue (Ashima something) as his patron, another used to work for the Obscurati facility in Cauldron-Hill in his past Deva life and used to be Tinker's teacher but doesn't remember it because it was his previous deva life, so that kinda stuff. One great example I read on this forum was to have a female Eladrin party member with amnesia actually being Kasvarina who had escaped Cauldron-Hill. These are just some examples.
These kind of links are making the world feel much more alive
Edit: spelling