Any ideas for a campaign (D&D3.5)?
or you could go plot light, and treat it as the tutorial area in an MMO. :) don't even have your friend roll up a character. just give them stats that are above average all around but don't scream one class or another.
have them wake up in a cave over looking a town in the distance they don't recognize and with no memory of who they are. gear, presumably theirs, has been tossed to one side and rummaged through, apparent robbery, no armor or heavy weapons. just a dagger maybe or quarterstaff. so they collect their things and likely head toward town. have a bandit attack on the way, something simple to demonstrate combat. something not very dangerous, maybe a drunk bandit who forgot his weapons and picks up a stick on the ground to fight with. after killing said bandit, the traditional search for treasure (or in this case, clues) turns up: some money, a few items, and a scroll. they read the scroll and find two things: 1) it's a magical scroll of fireball; 2) apparently they're a wizard of some sort. they get into town and the town is under attack by the rest of the bandits who happen to be threatening some townsfolk outside the inn. have the bandits see friend from a distance, recognize them, and charge. they have to move a couple rounds to reach your friend though (demonstrates in combat movement, etc). hopefully your friend remembers the fireball scroll they so conveniently picked up, and uses it. roast the bandits who all conveniently fail their saves and die. now friend has to interact with townsfolk to try to figure out who/where they are, what's going on, etc. maybe find a local priest to have injuries healed.
well, i think you get the idea. you can take it from there and expand if your friend isn't quite ready yet, maybe they're actually higher level and have levels in priest too. they could try out casting divine spells in addition to arcane after running into an acolyte who recognizes them and suggests praying for guidance (and thereby gets their divine spells for the day). maybe another bandit comes in the next day and attacks and then friend finds their spellbook on that bandit the next day. they now can memorize spells, but have to choose which ones (thus seeing the difference between divine magic and wizardly magic since couldn't memorize without spellbook).
after tutorial is finished, let your friend (if they want to) create their own character to start a more traditional campaign, or keep going if you/they're having fun.