I blame Phlox, for many things but especially this post. I've used all these tricks in my games at some point or another and I think they all work well.
1. Give the PCs a pet with a twist. The baby dragonling is ill and needs a rare herb that only grows somewhere dangerous. The goofy talking ferret is a secret agent spying on the party.
2. Give the PCs a ridiculously powerful single-use magical effect right at the start of the campaign. Once they use it, let it accomplish exactly what they hoped for, but also create unforeseen consequences.
3. Let players describe their hirelings when they're hiring them- "so before you stands a crowd of misfits and swords-for-hire, what kind of scoundrel are you looking to hire?" Then make sure the hirelings are funny.
4. When given a chance to humiliate a dickhead authority figure, the PCs will go to incredible lengths to do so.
5. Every city needs a magic tattoo parlor.
6. Have a list of fantastical foods and drinks on hand, and describe them on equal terms as mundane ones. Players go crazy for cocktails that turn their PC blue or whatever, and it adds texture to the world. The Gourmet Street zine is great for this.
7. Low-stakes contests are irresistible sidequests.
8. Every encounter table should include representatives of every local factions, as well as rarer encounters with wider-scale factions. And every place has at least three local factions.
9. Remind PCs of their reputations as often as possible.
10. If you need a unique NPC with absolutely no prep, just imagine them being played by a cool actor you like. A generic wizard is a lot easier to characterize when you decide she's being played by Pam Grier.