Coming from someone who has redone their game's introduction 14 times and tried 4 different main characters perspectives as the focal with which to view said introduction; I can tell you what worked and didn't work for me, though the helpfulness of such advice is subjective at best.
1. Less is always more: players won't know anything about what is going on to begin with and showing them an exposition of important characters before they start playing probably isn't going to do anything for them. Once you get people interested in the game is the time to really start building up the world, give them enough to know what to do next but don't try to fit the protagonists entire life of experience into an introduction.
2. Optional conversations are awesome: not everything that doesn't advance the current plot is useless information, but not everyone will appreciate that. My game starts from the perspective of a mercenary captain and the men and women in his troop. (Six mercs + current client) during a job to hunt down and capture a dragon. Within the game world these men and women trust and respect each other, but no amount of 'plot centric dialogue' will be enough to portray that correctly to the player, thus friendly tavern banter and roadside comments are engrained into my game at this point, most of which are interesting but none of which are required to progress the game.
3. Make npcs useful: what better way to immerse players into a made up world than to give them colorful characters and interesting sidequests to interact with? Injecting lore and information on the game worlds past/present into npc and quest giver dialogue/objectives works twofold, it gets your information out and typically prevents sidequests from turning into 'fetch quests' though it's also a lot of work to organize.
4. Keep the long exposition, just don't put it in game: at this point I've got over 500 pages of just exposition and lore building about my current game world (though the game was originally born as a 326 page novel) and I look back on it when necessary and keep it all organized with a timeline, but it doesn't clutter my game. That way the ideas are there to be used when applicable, but without having to force any of it down players throats. A lot of the information needed to create a believable world isn't even stuff that needs to be in game, but it's good to have to make sure everything is consistent throughout the plot.
With these thoughts in mind the prologue I've finally decided on and am happy with unfolds thusly: start around a table at an inn, approximately two-three minutes of dialogue telling the player who these people are and what they are doing; then a tutorial tip singling out one character that will provide tutorials on gameplay if asked and suggests speaking with everyone else as well. Player then assumes control, can chat with party members to get a feel for who they are and how they feel about each other, they can spar with the newest recruit and learn what my game had that is different than standard fare or they can walk out the door and advance the plot without participating in the world buildingaspect, instead only dealing with more plot-centric information (though I wouldn't recommend it since the game is pretty much character driven, the point is though that they can get to the action and come back to soaking up all the rest at their leisure.) so the introduction to my game can take as little as 5 minutes or as much as 40, depending on whether the player is actually interested in learning about the characters and their motivations or is just interested in getting to the gameplay.
