We of the Naruto fanbase have met plenty of characters throughout the series. We have also seen the various roles ninja can be. The major things they can be are
1.) Regular ninja, go on missions stuff like that.
2.) ANBU ninja, assassination, information gathering, etc.
3.) Sensei to younger ninja. (kakashi style)
4.) Sensei to possible ninja (Iruka style)
6.) Tracker nin.
7.) Torture and interrogation.
(I'm pending putting medic nin up here, if one more person says they want it up here I will.)
And I think that's basically it.
For instance, I think, with a little training, Naruto would make an excellent teacher, Sakura a good regular ninja, Sasuke a member of the police force or a member of the ANBU. Go ahead.