There is a surprising amount of detailed combat rule information in both AD&D PH and DMG if one bothers to look for it. I don't recall us ever doing so 'back in the day,' but it is quite usedful to me now. Evidently, the only rule permitting movement and a melee attack to occur in the same round is the 'CHARGE' rule. If anyone can shed more light on this, please do so, only note that I am only interested in the rules as written, not house rules.
Unfortunately, the combat rules are often more of a collection of ad-hoc rulings than a system as such. There are "rules" in the PHB that really should be in the DMG but didn't make it in. And the PHB has references to rules which don't appear in the DMG at all!
Anyway...
Movement in combat is quite interesting. To a large extent, it doesn't happen.
* A character may move up to its movement speed if not in melee.
* A character may attack in melee if within 10' of the combat.
* A character may charge into melee, moving at 200% rate (if indoors) or 133% rate (if outdoors), with a +2 attack, no Dex mod to AC (and a 1 penalty to AC if no Dex).
* Once in melee, the character may not move, except by
...fighting withdrawal. The character makes a retrograde movement (possibly of up to 50% speed, but not defined in PH or DMG) which can be combined with a parry. If his foe follows, the foe may attack (and possibly also the character).
...disengage. The character moves at full speed away from the combat, allowing engage enemies to get a free swing against his back (no Dex, +2 to hit).
Parrying adds the character's Strength modifier "to hit" to the AC and no attack from the character. Yeah, really not worth it. I suggest the Basic D&D rules of a 2 bonus to AC.
A cleric can both attack and turn undead in the same turn, but may not turn undead and cast a spell.
For those who want to really enjoy morale rules, the "retreat" result can be interpreted as a disengage plus a 50% chance of the combatants dropping held objects...
Cheers!