I would say that if you are a positive person, this would in most likelihood make you more likeable. If you are a positive person, you are constantly looking for the positive in others, and genuinely liking someone else, or at least showing that you like them, makes you more likeable. Similarly, I think the opposite is also true. The phrase 'don't shoot the messenger' comes to mind, as we have been shown to be less likely to be liked if we are the bearer of bad news. Positive people are either able to or are inclined to put a positive spin on things that could be construed as negative. This would mean, even with the giving of bad news, depending on how it is portray, they could still be seen in a positive light, which makes them more likeable.

Obviously I've been reading a bit of psychology, and obviously again I am generalising, but in my own case, I have found this to be true. I tend not to share bad news if I can avoid it, or if I do, I always try to see the positive in it, and I always try to portray that positiveness to the other person. A lot of this is because I don't want people to pity me, so I try to show them how even though the situation is bad, I am still thinking positive, and that I honestly do think that things will be ok. They might not be the same, but they will always be ok. I have also learned firsthand that humans have the uncanny ability to come to terms with at least most things, if given the right amount of time.

This sort of mindset I think means that by nature I am a positive person, and I think this leads to more likeableness in general.