Here are the rules I'm using for my current character, a hedonistic bastard who would be magnificent (but usually isn't):
- Only allowed to use enchanted, charged weapons.
- Cannot recharge weapons. Out-of-charge means broken.
- Cannot swim in armor unless using a water breathing effect. If he falls into the water while in armor, he must ditch the armor. (He spent all night naked in the wilderness after getting dumped out a waterfall once. Good times!)
- Must always be trying to buy something. If he's gained over 10,000 gold, he's probably doing something wrong. Greed is good! Frugality is bad! When in doubt, buy and drink all the booze in town.
- Sleep every night. Never wake up before 10.
Here are some things I try to stick to, but they're not rules, per se:
- Replace armor after particularly intense dungeons. (Is there a better way to simulate armor breaking?)
- Always have a substance to abuse at night (alcohol and moon sugar derivatives).
- Avoid fast travel. Note: Fast travel is okay if you know there are no radiant event spawn points between you and the destination.
- Always go for the short-term gain. Be completely blind to long-term benefits.
- If you come close to death just before killing a boss, maybe drop your weapons and wait for 10 hours or so to simulate recovering from a severe injury. I lost a sword this way. Getting back to town was quite an adventure...
Well, what do you guys do? I would've posted in a thread like dead-is-dead, but I don't actually play dead-is-dead. My character is far too dumb to live, after all. (And that's the fun of it!)

or if my follower disappear...), but the general rule is No Fast Travel.
My last character didn't have any of these rules, but she had an insanely cluttered journal from all the quests she picked up that she would never finish for her own personal reasons.