Negativity usually arises from an attention to the past or future.
When we attend back or forward in time, we often reflect about how it could have gone better, or anticipate how it could still go wrong.
Positivity, on the other hand, usually arises naturally from an attention to the present.
When we look around us in an accepting and non-judgemental manner, we allow ourselves to notice and savour the little things that help make life beautiful, wondrous and up-lifting.
Whether it is the song of a bird, the blossoming of a flower, the sound of our own breath, or the smiling face looking back at us, the present moment is almost always filled with positivity.
If you want to increase the ratio of positivity to negativity in your life, it starts simply by being conscious about where you are placing your attention.