About the story and the type of game:
It really depends on their taste... I've used Eberron premade adventures to great success to introduce D&D to some of my friends leveraging their love for "pulp/steampunk" games like Hollow Earth Expedition and Deadlands.
Just try to think something they like or the gameplay style they like more if they've already played other RPGs and make it "familiar" to them. Still try to mix in a bit of everything a bit at a time so they'll get a nice overview of all the aspects and parts of the game.
About the characters:
Avoid giving them full spellcaster classes, at least for the first levels since D&D rules aren't that simple (or few) and full spellcasting requires quite a bit of skill and knowledge (of the game, the rules and the spells) to be used effectively. Wizards and Archivists especially made more than a newb of mine run away scared and whine about it being too weak and useless (true story!).
Sucky classes (considering "almost none" to "none" as far as optimizing and multiclassing go - at least for the first game) and one trick ponies like Monk, CW Samurai, Barbarian, Fighters, Paladins, etc should IMHO be avoided too.
Cleric is an exception since it works quite well anyway (even if you pick bad spells you could always convert them into heals, and you're still a gut in a fullplate with a huge axe, no cloister tho, since you don't want them to go healing into melee with a leather armor).
Other than that ToB classes/PsyWar/Ardent/Stalwart Battle Sorcerers/Mystic Ranger from Dragon Magazine and other hybrid classes like those are a good "intro" to spellcasting for people who like it (basically anything that can cast, doesn't have a huge list to choose from or spontanous casting AND a fallback way to be useful is good). Those classes have also the huge bonus for first-time players to work somewhat well without any multiclassing or minmaxing.