Each Clan & Career have their own specific way of leveling up:
Every point counts as 1 level (Subject to Change).
Careers
Anbu: Every successful mission is a level (S-5, A-4, B-3, C-2, D-1,).
Bounty Hunter: Points are given for successful hunts, based on rank (S-5, A-4, B-3, C-2, D-1).
Medical Ninja: = Chakra control.
Samurai: Weapons points (Every 3 is a level).
Clans
Aburame: = Summoning Jutsu level (Kuchiyose)
Uchia: = Fire Element Mastery.