Given the number of new-to-tabletop gamers I get, I decided to keep the rules system as simple as possible for 2nd edition(which is surprisingly pretty simple when you realize just how much of 2nd edition is actually just optional rules)Ability Scores: In order to make character creation faster, I decided to just go ahead and let the players use d20's elite array(15, 14, 13, 12, 10, and 8 arranged to taste). It keeps the players relatively equal, even if they are a little high powered for my taste. I should note, I ignore the maximum spell levels as well as the maximum # of spells rules. To me they just seem kinda silly.
Races: The only 4 races I'm currently allowing are Humans, Dwarves, Elves, and Halflings. Humans are strongly encouraged. Non-humans are required to have an intelligence high enough to know 2+ languages so they may speak common in addition to their racial language.
Classes: Only the 4 core classes are currently allowed. Yes, that's right, 2nd edition only has 4 core classes(it says so right there in the PHB); Fighter, Mage, Cleric, and Thief.
Multi-classing/Dual Classing: If the race allows you to multi-class with the 4 classes, go for it. I got rid of the super-high ability requirements for dual classing, so if you're a human with the stats to qualify for the class, and a good RP reason for becoming a different class, it's easier to do.
Proficiencies: I'm keeping languages, but getting rid of the vast majority of proficiencies. Clerics and Wizards may learn to read and write in all languages they know by spending a language slot(language slots are . Fighters and Thieves may learn to read and write by spending a slot for each language they wish to be literate in. As for weapon proficiencies, everyone knows how to use all the weapons and armors allowed for their class(es). Single class fighters also get a "favored weapon" which is just, in effect, free weapon specialization for one weapon.
Equipment: In an effort to keep character creation simple and fast, I created the starting equipment lists. I enforce their use, but I'm willing to work with a character if he wants a different kind of armor or weapon based on character concept.
Encumbrance: Like every gamer out there, I have a love-hate relationship with encumbrance. This is usually handled on a case by case basis. For long term games, yes, I use it. For one shots or for games where I don't think the player is going to stick around, I ignore it.
Hit Points and Death's Door: I make players roll for HP, even at 1st level. I also jettisoned the death's door rule. To say I despise superheroes is an understatement. Max HP and Death's door seems to promote that sort of play.
Initiative: Core rules says initiative is rolled per side, and casting time/weapon speed is optional. So it depends on how many new players I have that determines which initiative I deal with.