From my notes on designing such:
* No extremely long-lived or short-lived races. 40 to 100 years of expected age of death for everyone past puberty is ideal.
* "You finished your adventure/levelled up. 3d6 seasons pass without much of anything interesting happening ..."
* Solid genetic inheritance stuff is required, but doesn't have to be more than a bunch of weighted random tables.
* Use webtrees to keep track of everyone of note as well as events.
* No rushing. Plot lines are allowed to take decades to finish.
* Blow up everyone who thinks inventing gunpowder means they're free to build tanks next.