I'd like to be happier.
I think the main thing that contributes to a positive person is that they have one main objective in their mind -- to be positive. A positive person tries to find a light in trying times. When something is difficult or going wrong, perhaps they remind themselves that things CAN work out if they keep trying. When something seems impossible, they keep hope that all things are possible. If others around them are worrying or having hard times, perhaps they remind those people that things won't always be so difficult. Maybe they offer to lend a helping hand. If things do go wrong, which they sometimes will, a positive person will say "we can try again tomorrow", or they will remind themselves that they tried their best. This also applies to other things, of course. The main idea is to keep negative thoughts away, and to try to inspire yourself or others around you when in most cases it's really difficult to see it in a positive way.
Good points, Mel. Another point I'd like to add is that you have to look at things from a realistic point of view.
You have to realize that things do go wrong and that we don't always get what and when we want. And although we do have dreams, some won't come true. Realizing that lessens the impact of disappointment and helps you get over it faster.
I hope that made sense.