I put this explanation together a few months ago for my new group:
Pre-1985 AD&D
1st Edition Pre-Unearthed Arcana (PHB & DMG only).
No Non-Weapon Proficiencies. No Weapon Specialization.
Note that Monster Manuals I and II included additional Races several years before Unearthed Arcana was published: Mountain Dwarves, Gray Elves, Wood Elves, Grugach Elves, and Valley Elves. [The additional Elves are rare and isolationist enough; I’m also not including the Underdark Races.]
A Natural 20 is an automatic hit or Save. (No Critical Hits)
A Natural 1 is an automatic miss. (No Fumbles)
No random social class table. “All PCs are assumed to be freemen or gentlemen (or able to pass themselves off as such) unless the DM places them otherwise.” [DMG p.88]
Damage: Unconscious if a single attack drops you down to zero to -3 hit points. Otherwise, -1 hit point per round at negative hit points until death. Permanent maiming at -6. Death at -10. Stopping the negative hit point bleed-out consists of binding wounds, starting respiration, administering a draught (spirits, healing potion, etc.), or otherwise doing whatever is necessary to restore life. [DMG p.82]
Then, natural healing is a very slow process and characters may be laid-up for weeks. I’d argue that “spirits” probably won’t help someone unconscious and bleeding to death as alcohol only grants a +1 to +3 hit point modifier at the most severe imbibing.
Elven meditation in lieu of sleep was introduced in an unofficial Dragon magazine article by Roger Moore and was later a 2nd Edition addition. It did not exist in the core AD&D 1e books.
Ability (Attribute) Checks aren’t really that common and aren’t even part of the 1e rules, and the DM shouldn’t call for them every few minutes to see if a PC notices something. If the DM tells you that you found a secret door, then you need to figure out how to open it, not make an Intelligence check or a Find Traps roll. There is some meta-gaming conflict as on one hand we have “Your character doesn’t know what you know” yet on the other hand you’re supposed to figure out problems as a player. That’s perfectly fine. However, a player who knows a lot of trivia shouldn’t be able to turn his or her character into “A Connecticut Yankee in King Arthur’s Court.”
Plus, we already have game mechanics that cover “Ability checks”: Strength has Open Doors and Bend Bars/Lift Gates. Intelligence allows Magic Users to comprehend a spell formula well enough that he or she can memorize it from a spellbook. Wisdom grants will-based Saving Throw modifiers and provides a chance of spell failure for “unwise” Clerics and Druids. Dexterity grants dodge-based Saving Throw modifiers (yes…see the fine print in the PHB). Constitution has System Shock Survival (surviving Petrification, Polymorph, and Aging…it’s not a 5e Death Save!) and Resurrection Survival. Charisma has Loyalty (Morale) and Reaction rolls. [The Basic set suggested a DEX check to climb ropes…as opposed to a Thieves’ Climb Walls.]
Fire Building: Only requires Tinderbox w/Flint & Steel. I’ll point out that Tinder can vary greatly from dried grass to cattail fluff to char-cloth to pine tree fat-wood to birch bark to feather-sliced sticks, and so on, but there’s no need to play this out.
You’ll need a readied flame to ignite flaming oil bottles or puddles, etc., not flint and steel. [FYI…you can’t make Molotov cocktails out of olive oil and tallow. Flaming oil and food/lamp oil should be two different things...unless you want your bullseye lantern to explode every time you drop it on the ground.]
Swimming: Everyone can swim. [For drowning, see DMG p55]
Hairfoot Halflings are afraid of water, so I’d rule that they can’t swim. [Monster Manual]
Getting Lost: [See DMG p49]. “Becoming Lost: Any party not guided by a creature knowledgeable of the countryside through which the party is moving, or which is not following a well defined course (river, road, or the like), or which is not using a well-drawn and correct map, might become lost.” [Knowledgeable would include locals woodsmen, caravan personnel, Rangers (skilled in “woodcraft, tracking, scouting, and infiltration and spying”), and Navigators. Also, Gnomes have a chance to sense direction while underground. (But not Dwarves??)]
Riding - DMG mentions that fighters should be regularly practicing riding as one example for the proper playing of a fighter. However, everyone (at least Player Characters…) should be able to ride. (And Aerial Combat: To be able to fight while flying any aerial mount requires considerable practice. To become adept at aerial archery entails at least two months of continual practice.)
Note: In the Monster Manual, Elves do not favor horses and horses are not mentioned in their lair description. They’d tend to be on foot, even though the World of Greyhawk Glossography puts them on warhorses. Gray Elves might know how to ride griffons and hippogriffs, though.
Secondary Skills: [DMG] “As a general rule, having a skill will give the character the ability to determine the general worth and soundness of an item, the ability to find food, make small repairs, or actually construct (crude) items. For example, an individual with armorer skill could tell the quality of normal armor, repair chain links, or perhaps fashion certain weapons.” (As DM I would also refer players to the Hirelings chapter for relevant additional information and potential downtime pay.)
Equipment Lists by Location: “Gygax favored a small sack slung over the shoulder, holding holy water, potions of healing, presumably at-hand for quick use during melee…also iron rations, wolvesbane and, small silver mirror, tinderbox…” [Online comments about Gary Gygax’ Player Character Record Sheets]