How I would write one
Frozen ocean, frozen river, ice wasteland, huge biomes (3 types of biomes because the huge biomes controllor needs three to be stable)
Flat (terrain type)
Half length, Normal Sun (Time modifier + sun)
Half length, Normal Moon (Time modifier + moon)
Normal stars (Stars)
Eternal Snow (Weather)
Dark (Lighting)
Clear modifiers (to prevent a bug in the current version from ruining all your hard work)
So that would create a winter wonderland, with 5 minute day's and nights, and give you a stable age.
That's the bare minimum, you can add things to it, say have four suns all moving different directions with blue clouds and a pink sky, and that would still be stable if you wrote them all in correctly.
If you become greedy and for example, make tendrils of diamond ore, then your age would become unstable.
Adding in valuable resource features adds instability, dense ores adds instability
but you can counteract those by adding in say, charged. This is kind of a choose your poison thing, so adding in normal instability effects willingly means there's less likely to be any other that you don't expect.
Have a look at the mystcraft wiki page if you don't know how to use a page you get
http://binarymage.com/wiki/doku.php?id=writing:symbols