House Rules

0) Don't play against the AI.

I've not deliberately changed anything to make it this way all the time, but when I set things up I like as much randomness as possible - so I allow races to start in the same system, and I also allow random homeworld sizes. When you start on a middling quality tiny world, that makes things interesting at the start - I had about 550 research per turn, no room for organics and radioactives, no intel, and slow production. No other planets in-system were very good either. It was great starting like that I may see if I can make sure I always do.
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"No greater love hath a man than he lay down his life for his friend. Not for millions, not for glory, not for fame... for one person. In the dark. Where no one will ever know or see"

Jack.

OK, I may have exagerated a little bit...
Many multiplayer games forbid tech trading.

When I play hotseat with my friend, I ALWAYS add at least a fighter fighter bay on to each of my non-frigate attack ships so that I can always travel with a fighter escort. I don't do this in single player. Also, I don't use mines in single player either. (although both of theese are fine for multiplayer )
Also, actually designing big ships instead of light cruisers and destroyers and frigates is good I guess. In single player I tend to build story driven ships

"Those stupid phong wont know what hit them as our new dreadnaught rolls out of the shipyard. Firey death be upon them!"