I think the best solution would be to have a clear goal. Not just endless RPing and 'Simon sez' games, or finding a random loving sword beneath some boxes, but to work towards something.
- Jailmates: Good conduct = faster discharge?
- Guards: Fewer people killed/injured while enforcing rules = more credibility?
There'd have to be some sort of definite structure, so that the entire game doesn't revolve around the boredom or imagination of its players.