Mentor spirits add a ton of flavor, including both advantages and a disadvantage, for a reasonable price. They can be a good place to start a character concept, especially for a street shaman.
ShadowcatX has the basics of the optimal mechanics. Magic, spellcasting, and summoning should be as high as possible. Perception, Sneaking, and Counterspelling come next. If they're playing a shaman then they'll need a decent Charisma score (for soaking Drain) so that usually means a handful of Social skills are worthwhile to take advantage of the high Charisma.
There are lots of threads about what the "best" spells are. Coming up with a list of 10 that touches on each school of magic (Combat, Detection, Health, Illusion, Manipulation) should be easy. A couple spells from each school will make the character flexible and useful in almost every situation. I think it's worth 10 karma to pick up another 2 spells at the start of gameplay for the added versatility.
That's the broad outline. If you (or he) have specific questions or concerns then we'll be happy to address them.