I have to admit my... tastes, criteria is maybe a better word, are a bit different than in a lot of dealers.
We do tend to clean cut, and almost over-friendly types.
For service advisor, make a point of your typing skills, having a good memory for numbers (if true

), and especially good English language skills- so there would be few mis-spellings on Repair Orders, clear phrasing, good representation of the complaints that are bringing the car in for service, and that you can communicate with those who are heavily accented.
Keeping a cool head and resolving conflict, as well as having a thick skin come in handy- there will be a customer most days who comes in just looking for a fight. For this reason, we often tend to older fellows- two of the best I've worked with are retired from the forces- cool heads, easy conversation about Canada, etc.
One thing to watch is many dealers have incentive programs that you are paid bonuses on engine flushes, coolant flushes, transmission flushes, alignment checks, etc. Sometimes you'd feel your ethics under pressure. Be aware that the ideal situation is a straight salary, or a bonus based on department sales, or something more generalized. Of course, it's difficult to make your own pay package during an interview, but just a head's up.