The final trait of a truly likeable person, without which the rest are ineffectual, is realness. This means being genuine, true, and authentic. In other words, show some humanity! No one is completely cheerful or relentlessly upbeat all the time. If you're always chirpy, people are going to think you're fake (or on medication which they will ask you to share).
But how do you show your humanity without becoming a complainer or whiner or jerk? A sense of humor goes a long way toward being real. The best kind of humor? Self-deprecating. Making fun of your own shortcomings is a sure way of showing people that not only are you not perfect, but you're willing to point it out. Someone who can laugh at their mistakes is very approachable.
I personally used to be perfect, but I've deliberately cultivated a few foibles in order to be more believable.
See what I mean? That's self-deprecating humor.
I also strongly express my feelings but mainly about inanimate objects. I have a very famous and vocal "hate affair" going on with the color copier at the Clovis Chamber office. This highlights my realness and no one's feelings get hurt (I don't say a word when the copy repair guy is there).
Realness is the key trait that takes you from "nice" to likeable. People who are nasty or hateful sometimes justify it by saying "hey, I'm just being real." Yeah, they're real, but without any friendliness, relevance, or empathy, I'm not going to like them.