How Can I Start Thinking Positive?

I've noticed that throughout the day I go through a variety of moods.
Is there a particular mood that you consider to be ideal?
My ideal mood would be happy, positive, filled with energy, focused, and maybe something else.
I am never in my ideal mood.
Suppose I am in a non-ideal mood, or bad mood. What should I do to change my mood?
I'm trying to get a girlfriend.