Because I misread the title, my thought was that you were going to roleplay characters leveling up in a sort of 'training montage.'

I used something similar in my last Freeport game, assigning each of the players someone to serve as their mentor for training up, learning new spells, feat training, etc.

The Fighter ended up with Bill Sangalapulatele* as his mentor, a polynesian shark-toothed ex-cannibal-turned-bodyguard with Fighter and Monk levels. The Fighter wanted to learn the Dodge feat. Bill started throwing coconuts at him, saying, 'If you can dodge a coconut, you can dodge a sword!' Once the player quit laughing, the game continued.

The Druid started with the Blooms, a pair of anarchist hippy-types who grow and distribute herbal drugs from their herbary. They were pretty unhelpful, and got him in trouble with the law, and he ended up working with a dwarven botanist across town who also had Druid levels named Dordenden.

For a city-based game, it worked great, forcing interaction with the city locals, and getting the PCs tied up in local affairs. (The Druid ended up going on a mission to rescue a kidnapped visiting dwarven Prince named Thorgrim, who was being held by a corrupt city official, and so couldn't be 'officially' rescued. The Fighter PC encountered other member of 'Bill's' former tribe, working a child-slavery ring, and still quite fond of filing down their teeth to savor the 'long pig.')

Each NPC mentor also came with advantages. When the Druid started wondering how he could improve his armor class, Dundoren showed him an alchemical technique to adapt the work that went into making Darkwood Shields, and instead fashion them into Darkwood Breastplates. The Wizard's mentor, a prematurely-dotty (and very hot, for her age) alchemist / transmuter named Delinda, also ended up dragging her occasional student into some intrigue.

If your game isn't city-based, this sort of thing is going to be harder, obviously, but there should still be missions and quests that will only get awarded to those who curry favor and impress the quest-givers.

If the party never chats up the local priest, they won't be the people he calls upon when a ghoul breaks into the reliquary and sneaks off with the corpse of a knight for snackage, incidentally taking an important relic that blesses the area and wards off disease in the process. They'll instead be treated to seeing some other adventurers, who do have social skills and have learned how to talk to girls and stuff, get these sorts of missions, and being paraded around the town square as local heroes, while they are left reading the posts in the town square to see if there are any caravans that need guards for 5 sp a day...

If the party Rogue doesn't make nice with the local guild, he won't be 'cut in on the action,' and he might be peeved to hear through the grapevine about the 'bandit raid' on the local taxman that happened far outside of town (so that the town can't possibly be blamed for it) and to see how the local rogues are spending gold like copper on hard drink and soft women, flush with their success.

Have the PCs roleplaying lead to the quality of their missions and the rewards of those missions. If they don't want to roleplay, then let them do the meat-grinder they want to play, there's no reason to punish them, but toss out occasional references to local heroes *who aren't them* who are getting exciting missions, free gifts from the grateful people, and townsfolk throwing their unmarried daughters at them.


*For those familiar with these Denizens of Freeport characters, I changed most of them. Some a little, some a lot. I even changed Bill Sangalapulatele's name, because I found it easier to pronounce with the extra syllable, and he certainly wasn't a tooth-filing ex-cannibal before I got my hands on him!