When I create a character, I start by picking a social status, one story flaw, one personality flaw and one learning virtue then I stop and I consider options arround the concept I have in mind. There's usually a Puissant something somewhere and a Focus is always nice to have.
But a new player who doesn't know ars magicka at all? Funnily enough, the one thing I don't do during the first game session is giving them the book. Ars has a steep learning curve, and the last thing I expect a player to understand is how spontaneous, ceremonial spontaneous, formulaic and ritual magic work after game 1, let alone what virtues and flaws might be useful.
This was how I did my first game:
The second time we introduced a player in a saga, I was not the gamemaster that time, but again, instead of giving her a full fledged magi to build, what we did was introduce her as an apprentice and she learned about the game as I opened her arts and taught her how to create her first spells.