You have no choices when you level up.
You unlock new skills/passives/runes, but they're always unlocked at certain levels, you never have to choose.
Your only choices in this game are what gear you want to wear, and what skills/passives/runes you want to use right at this very moment, since you can change any of those things at a moments notice.
You don't pick which skills to unlock, and you don't pick where to allocate your stats.
When you level up, just check what new thing you've unlocked and decide whether you like it better or worse than what you're currently using.