Post your houserule(s)

I let the AI handle all combat that it is capable of (excluding certain territory like Norway or Finland where it has problems, or amphibs). I often let the AI handle trade so i cannot unrealistically stockpile. I never DOW a nation or prolong a war for better laws.

No more than six beers in a playing session. Any more than that, my strategy, tactics, and soldiers suffer!

Serious Note:

Historical start dates. I like to start campaigns on their historical start dates. Especially playing as Germany and Japan.

Historical ministers. I research when certain ministers came to power and insert them whenever possible.

That's about the only ones I have.

I like when playing majors to basically over the course of the game research everything (as a Major modernizing nation would) regardless if whether i plan on building them or not. This eats up alot of LS as i dont wait until the end but tend to do it as the game goes on.

Compliments on the thread--I have wondered about what others do.

I use mostly the same rules for myself in MP or SP games.

1. Not less than 5% of available leadership is allotted to any area throughout the game.
2. Leaders cannot be demoted. Promotions will follow a natural path with at least one (need exceptions here and there) new skill level before promotion can occur.
3. No new FM's are created unless all existing ones are being used-I must find a job for even the worst.
4. If a SP game; check my primary enemies for gross leader errors. I only spend perhaps 10 minutes fixing a nation--so only obvious errors are fixed. Key commanders are promoted and given correct ranks for their assignments.
5. No "Decrease Unity" intell missions prior to war.
6. Maintain a balance between the various services to what seems historically reasonable--no spamming a unit type to the irrational detriment of the other services.
7. No non port amphibious invasions.
8. No setting large operational traps against the ai (leaving beaches open for instance).
9. If playing Germany-the 2 BC's must be built using the '36 techs and the 2 BB's must be built using the '38 techs-and those must be built. I do not let the BB's "launch" before the approximate historical dates. Occasionally I will drop this, but only when I fully intended on skipping my normal, somewhat historical, early war operations that match RL.
10. Not really a rule, but a habit; SPR winning the civil war ruins my game--so I don't let it happen. I give appropriate aid playing as Germany or Italy. However, if the Nationalists are clearly loosing, I will tag switch to SPR and delete all non HQ forces--then check for new ground units in production. IF new units are almost ready--those go bye bye too. If you're gunna do it, might as well do it right.
10. No tech rushing--which eliminates any nukes prior to mid 45.
11. I make sure enemy majors are researching important techs that they should be (or did).
12. A cabinet position can only be changed once per year at most.

If something seems gamey or not historically plausible, I avoid it.
I have tried letting the ai take care of trade, but just can't stomach it (playing as Axis) for more than a month or so. That surely would make for a tougher game. Some fine day I will follow that all the way.