Be different. Characters who’ve already been seen in literature are not only boring, they’re unimaginative. But, someone might say, there are only so many characters in the world and they’ve already been done to death. Not so. Every character has different facets or habits. For example, Captain Queeg in Mutiny on the Bounty was a psychopath and, true, there are enough psychopaths in literature to overflow all the asylums. Ah, yes, but Captain Queeg rolled metal balls in his hand when he got under stress. That made him a psychopath like no other.
It’s not necessary to make a character like no other that’s ever been. It’s enough to give them traits, habits, tics or whatever that have not been seen. For a main character only one or two characteristics are needed, no more than three. For a minor character maybe one or at the most two. And be consistent. If a character is a skinflint, he can’t be in a scene and be generous on one occasion. The reader won’t buy his personality from then on. The only exception would be if he pretended to be generous into order to deceive someone or gain an advantage, but the reader knows why he’s being false to his true nature. Not only be consistent, but remind the reader now and then by intentionally inserted stingy acts to fortify his character trait and remind the reader who he is.