What I've been finding works well from a story-arc perspective is to
have a separate track of character-based goals with ladder levels
attached to them at CG. As those resolve, they have a test against
that new level from the one they want to improve. Success means that
the trait/aspect/whachamacallit is at the new level.
EXAMPLE: I have Good kung-fu. I've just hunted down the last of the
bandits who desecrated my former training temple - a Great goal I'd
set as part of my background. I roll NdF and if I get at least +1, I'm
now Great at kung-fu. Fail, I'm still Good - I just don't get as much
reward for my accomplishment in the story.
Breakages: what if the goal level is set below the current level? I
say it's no longer eligible for use, but that sounds a bit Fiat to my
ears. What about using tokens to buff the roll? I'd say that's legit,
but again - sounds like an Italian automobile.