Improved worker conditions
One of the best generic ways to push stability. Was already adressed above.
You get a lot war suppport later with aces and propaganda decisions, so this can be worth it.
But I once almost had to demobilize (reduce mobilization law) because of Promises of peace once, so I'm healed for a while.
Anti democratic raids
Anti communiste raids
Raids are also good to push stability. You lose 10% and get 12.8%, a net win of 2.8% stablity AND some party support.
And compared to Improved worker conditions you dont lose factory output and dont need consumer goods factories.
Ban democratic parties
Ban communist parties
If you have maxed your base stability you can only get more stability by getting more party support.
Example:
When you have 80% stability in war (100% base, -30% war, +10% party support) and your base stability is maxed you cannot use Improved worker conditions or Raids to push your stability, because they don't push base stability over 100%.
If you ban democratic an communist partys you get your Party support to +15 and lose some stability.
Now you may be at 75% (90% base, -30% war, +15% party support) and you can push the 90% base to 100% and therefore your overall stability to 85%.
Not really worth it, but if you have nothing else to do...
Institute press censorship
Late game. You don't know what to spend PP on. With this you get a little +stability (because it pushes party support) with no drawbacks.
There are also some that gives 1 extra tile in a state - seems not usable.
Useful if are a small country and have no building slots. Here you get some. (But PP may be spent better for other things.)
Or if you need a building really fast and have only low infrastructure slots left. With this you can get a slot in a level 10 Infrastructure state.