While we don't have any other fully sentient people to compare ourselves to (that we know of...), we can point to animals and realize that they have intrinsic behaviors. Some of these behaviors have even been bred into them, in the case of domestic animals: look at the listed temperaments of different breeds of dogs and cats.
Now, for an intelligent fantasy species, like an orc or an elf, you can use similar types of temperaments as a biological basis--as long as you remember that temperament isn't the same as behavior. You can say that orcs are prone to aggression, or are hot-tempered, or are highly emotional. This means you can have an orc who is a violent, sadistic raider or merciless bandit... or who is a prized athlete, or is the leader of a rebellion, is a societal activist, or an artist who is famed for being able to make deeply emotional works.
So for each species you have, you can give them that sort of temperament. And that's how you make each one different.