I use this "level up" method:
Each player gains a training week for every session they play and learn one training week of whatever skill they use most. We don't track this in game we just decide what they used at the end of the session.
This method should lead to PCs getting better at things they do. I add this to the standard training week the players get for every week of gametime. I don't make them train it just happens no matter what they do.
This system (sort of stolen from the old Doctor Who) might give you what you need without changing a lot.
Each player gains a training week for every session they play and learn one training week of whatever skill they use most. We don't track this in game we just decide what they used at the end of the session.
This method should lead to PCs getting better at things they do. I add this to the standard training week the players get for every week of gametime. I don't make them train it just happens no matter what they do.
This system (sort of stolen from the old Doctor Who) might give you what you need without changing a lot.