If you happen to be an experienced DM, and you're teaching D&D to someone, is it best to go with Players Handbook only, dungeon crawling, vaguely Greyhawk-ian standard D&D? Is it okay to add in more diverse mechanical material? More diverse thematic material? What if your normal game doesn't fall into any of those categories?
On setting--better to go with a published setting, or homebrew? Does it matter? Does it make a difference how weird the setting is? Is something like Eberron or Dark Sun, which both change various baseline assumptions about the world and how the game's played, better if its an established setting, so new players have a place to go to get a more solid grounding in it?
What if you really want to play something like Arcana Evolved, or Iron Heroes, but the only players around are new? Better to start them off with the basics, or is it okay to start them with the slightly off-beat stuff? In some ways, Iron Heroes might be easier to learn--none of that magic stuff to deal with. But how would learning it first change a player's perception of D&D?
What if you've got a mixed group? Some new, some old? Should you get the older players on board with staying core, to keep the group simpler for the new players? Should you let the experienced players use wacky supplements, but tell the new players to keep to the basics? Will new players even notice?
On new stuff--does it make a difference, in both whether to use it at all and who to allow to use it, whether it's new variations on old stuff or entirely new things? New feats and spells? New races? New prestige classes? New base classes? New subsystems? Are there some subsystems that are easier to use with new players than others? Psionics? Incarnum? Book of Nine Swords?
How much weird stuff should a DM use, when running a game for new players? Should you stay core, too? Take advantage of having some players who don't necessarily know that a troll has fire resistance? Or is it okay to go weird, since your players don't know the difference and aren't keep track of it? Is it okay to use PC parts in your NPCs that you aren't allowing the players to use? Is it okay to use subsystems that you aren't allowing your players to use? (Those last two don't apply just to new player campaigns.)