As usual, it depends on the character, but some of the across-the-board rules I like to apply include:
1. only carry what seems realisticly possible. Which means one set of armor and a limited amount of items in the invisible backpack. None of my characters ever get anywhere near to being over-encumbered anymore. Some items (usually potions, torch, or ingredients) can be carried on the character's belt. these are the ones I've got hotkeyed.
2. Melee characters must have only one weapon or weapon/sheild combo, assuming these items are large. Renee Gade and Renee Gade II, for instance, had a bow, a quiver of arrows, a longshield, a sword, dozens of potions & items... :facepalm: It's just ridiculous! Dyan the Paladin on the otehr hand only has her 2-handed sword or a longsword/sheild combo. Of course, this makes things interesting because she can't just switch to a bow if distance is involved...instead she usually tries to get NPC's attention by casting a Light spell and jumping around! This means the NPC now has to come to
her. Sometimes, she'll also CHARGE into battle to meet her opponents.
2. Occasionally when something particularly tasty is found (Sheid of Warding or whatever) my character will cast aside whatver sheild she's got at the moment...literally throw it on the ground and walk away! This depends on if she's gonna sell or keep the item she's picked up. As inconvenient as it sounds, I've left some items behind, gone back to town to sell or store something new, and then returned back to the dungeon to pick up the loot that got left behind (Glademist Cave, anyone?

)
3> the only exception to those first 2 rules is if there's a horse nearby. Let's say Dyan the paladin has found an enchanted curias, but she's already wearing a curias she's wanting to keep. She'll carry the new curias outside where the horse is, drop it on the ground, and go back into the dungeon.
4. No swimming in heavy armor... I mean, come on! No carrying any heavy weapons underwater, either. Matter of fact, I've had characters disrobe on a shore (or in a cave) go for a swim, and then return to suit up again.
5. All my characters walk alot (assuming they're not on a horse).
6> Since my Wanda Bone character, I've been applying D&D and TFT rules to TES. This means a character needs to have certain amount of intelligence or level before certain spells or skills can be obtained. This means a character also needs a certain amount of strength, before certain weapons are used. It also means Alignment (is your character evil, good, lawful etc) comes into play more forcefully. It also meeans one can't just pick up (let's say) a Repair Hammer unless one has been schooled in that skill first.
Since applying these rules from other RPGs, it's really helped because all my latest characters feel somewhat more realistically limited. No more "I've got the entire spell book in my hands because I can afford them all". If a character is supposed to be a weakling, no more swinging a longsword of any type (although Oblivion's Fatigue meter tends to prevent this anyways).
It's really somewhat of a relief to know it's possible to get thru Oblivion with just a handful of spell-types, for instance. Igodah Go^Pe had this HUGE spellbook by the time she started the MQ, for instance, but how many of them did she actually
use on a regular basis?
7). Finally, I like to "wait" alot to simulate time passed during some sort of activity. Like if one of my chars goes to the smith to get his or her armor fixed, I'll wait 1-6 hours, depending how much damage is needing to be repaired.
...from there, my rules tend to get more and more character-specific. Dyan the Paladin doesn't use poison or stealth-attacks...Beujok the Grey Wizard only uses silver or enchanted daggers, etc.