1. Calculating the XP Value for Monsters.
"You do not talk to me like that!! I work too hard to deal with this stuff!! I work too hard!! I’m a Division Manager in charge of 49 people!! I drive a Dodge Stratus!!" -Your DM, ruefully.
As much fun as we like to make of ye olde fashioned hobo-murderin', killin' stuff (through combat) has always been deeply baked into D&D. It is hardly surprising that the first part of the section on experience in 1e begins with ... wait for it ... defeating monsters. What might be somewhat surprising is just how discretionary it all is! To start with, Gygax stresses that the difficulty of the monsters alin should affect the reward of XP, and then provides the exact rule to use. It's pithy and simple to understand!
If the average hit dice or level is 10 times greater than the average level or hit dice, there must be an adjustment of at least halving or doubling the experience point (x.p.) award as the circumstances dictate, except if the lesser group is approximately 20 times more numerous than the greater value group.
See! Simple. Notably, Gygax also instructs the DM to award (subjectively) XP for outwitting monsters and overcoming traps or tricks, if it leads to treasure. In addition, there is a table (because this is the 1e DMG, and it has more tables than an IKEA Warehouse) that shows you how to calculate the base XP for killing/defeating a monster based on the monster's hit dice, hit points, special abilities, and super-duper special abilities.