Unified resolution mechanics
Traveller (1977) put everything into 2d6 rolls against a target number, but it was explained differently each time. The first landmark game was RuneQuest (1978), which made combat and skill use both into rolls under a percentile skill. However, it had special-case rules for combat rolls (specials, criticals, hit location, etc.). The solid landmark was James Bond 007 (1983), which had a true universal mechanic that used level of success in both combat and other activities.
Point build character creation
Steve Jackson's Melee (1977) first had point-based design. However, Champions (1981) was the real landmark design as fully building out the concept as a role-playing game.
Bushido (1980) deserves mention for its honor system, but that was followed quickly by Insanity in Call of Cthulhu (1981) and Psychological Limitations in Champions (1981). Insanity is integral but not very personal. PsychLims are personal but optional. After that, nods to Pendragon (1985) for an integral, personal mechanics for all characters.
Level of Success
RuneQuest (1978) introduced specials and criticals for combat. But James Bond 007 (1983) was the first to integrate level of success in every aspect of the system.
Hero Points - player resource modifiers to resolution
Top Secret (1980) had Fortune/Fame points which weren't really player-controlled. James Bond 007 (1983) clinched the approach, though. Ghostbusters (1986) had the dubious distinction of combining hero points and experience points -- an approach which usually doesn't work well, in my opinion.
Dramatic modifiers to resolution
Champions (1981) included bonuses for "surprise maneuver" which was a cool move as described by the player. But as for explicit modifiers for drama per se, I'd say Paranoia or Toon (both 1984).
Mechanics for social resolution
The landmark game was again James Bond 007 (1983) as the first game to handle social interactions as an integral part of the system. There were prior implementations, though, which I don't know as much about.
Worlds of Wonder (1982) was the first universal system in the sense of core rules + varying genre-specific add-ons. The next major landmark would of course be GURPS (1986) which really developed and popularized the concept.
Directed Rewards (other than for killing monsters or showing up)
There are rewards for skill use and/or training in Traveller and RuneQuest. Rolemaster (1980) greatly expanded what XP were given for. But the first to approach rewards as a way to direct play was Marvel Superheroes' Karma (1984), giving Karma for good deeds to encourage superheroic behavior.
Ghostbusters (1986) was the first to vary number of dice rolled as a primary resolution mechanic (i.e. not just for damage) -- the origin of West End Games' D6 System. This gives a much more tangible aspect to play, but summing 10 or more dice is cumbersome. Shadowrun (1989) introduced target number dice rolls which simplified the counting required.
Additive Fixed-Die Rolls
Virtually all early games, when they had a universal mechanic, used a mechanic of rolling under stat or skill (i.e. roll under skill on 1d100 or 3d6, usually). Rolemaster (1980) had percentile rolls plus modifiers and compared to a chart where 100 or over was a success. This became a more general mechanic with Character Law in 1982. Ars Magica (1987) used a universal mechanic of attribute + skill + 1d10 where the total is compared to a difficulty number (as opposed to difficulty being a modifier). Since then, additive rolls are now the standard for non-dice-pool games.
(Edited to add Rolemaster)
There were several games which concentrated on premade characters, notably Marvel Superheroes (1984). But the popularizer of templates was Star Wars (1987).
James Bond 007 (1983) has immediate rewards for hero points although not for experience points. As for all rewards being instant, I'm not sure.
Torg (1990) was among the first games to have explicit mechanics based on "scene". Probably Theatrix (1993) after that for making scenes central to the mechanics.
Meta-game control/Director Stance for players
Ars Magica (1987) allowed this through Whimsy Cards and troupe style play. Prince Valiant (1989) had more open-ended options in storyteller cards. Most fully was Theatrix's plot points and improvisations (1993).
Freeform Character Traits
Several earlier games had token nods at to make your own traits with GM approval as an option, but Over the Edge (1992) was the first to really take this as a primary method.
Player right to introduce conflict
I'd put this first as Champions (1981) for allowing the players to define their own Hunted and frequency of Hunted which show up on an objective scale rather than GM choice. But after that, Ars Magica, Prince Valiant, and Theatrix as in Director Stance above.
Well, that's about all I have for the moment. I'll eventually want to organize this all into a nice coherent article. But part two (game structure) is much more important, I think.