How to Stay Positive.

Visualize a Great Future:
You frequently run a mental movie of the future as you hope it will be or as you fear it will be. With conscious attention, you can choose what is in that movie. Choose to visualize a great future. Practice getting that movie back on a positive track whenever your mental movie of the future starts to focus on possible negative outcomes. Holding the mental image of a great future is the first step to creating that future.
Count Your Blessings:

Gratitude is the key to a great life. At any moment, some things are going well, while others are not going as we would choose. Being grateful for the blessings of life -- including the life lessons that come from our setbacks -- sets your mind for positive thinking and for enjoying a great life.
Be Grateful for All of Life:
With gratitude, all life appears as a blessing - without gratitude, all of life is perceived as a burden. Avoid the tendency to compare your life with the lives of others, with your idealized hopes for life, and with your own life when you were younger. Every moment of your life is a gift -- not something you are "entitled to" or something you "deserve." Practice zero-based gratitude. Zero-based gratitude is being grateful for everything in your life -- grateful that you woke up this morning, grateful that you have enough food to eat, grateful that you can walk and breathe and see.
Know that Life Isn't Supposed to be Fair:
No one is "supposed to" be nice to you or help you. No one is supposed to treat you "fairly." Storms, earthquakes, wars, flu pandemics, and falling boulders are not supposed to avoid you. Be grateful and happy when life goes well, and avoid anger and resentment when life is not "fair."
Avoid Anger, Resentment, and Regret:

Anger, hatred, resentment, and regret help nothing, and are a great cause of unhappiness if you allow them to infect your life. Whatever pain the storms of life ever cause you, anger and resentment can never heal that pain -- and they inflict their own pain - often a far greater pain than the first one. Whatever pain the actions of others cause you, anger, hatred, and revenge solve nothing -- again, the pain of your own anger often surpasses the original pain. Whatever pain you cause yourself by ill-chosen actions, regret solves nothing -- learn a life lesson, forgive yourself, and move on with life.
Forgive Everyone for Everything:

Whatever has caused you pain -- whether nature, others, or yourself -- forgive completely. Until you forgive, the anger you hold will continue to burn. The suffering will never end until you give up the anger and forgive unconditionally.
Keep Active:
If you are feeling depressed and negative, it is crucial for you to keep active. The less you feel like being active, and the more you just want to wallow in self-pity, the more important it is that you get out, interact with positive people, begin projects, and keep active. Until you begin to feel a desire to be active, just fake it -- go through the motions of keeping active until you can generate the positive attitude to drive your activity.
Choose to be Around Positive People:
Positivity is contagious - so is negativity. Choose to spend more time with people who think positively, speak positively, and support your vision, your life purpose, and your projects. Spend less time with people who talk about how hard and unfair life is. Spend less time with people who tell you that your goals are unrealistic and that you are certain to fail.
Be of Service - Help Others:

One of the best ways to appreciate your life and to create a positive attitude is to be of service to those less fortunate than yourself. Being of service reminds you of your blessings, keeps you busy with generous activities, and surrounds you with positive happy people.
Smile:

As with keeping active, smiling is something to do especially when you don't feel like it. Just form your face into a smile, take a deep contented breath, and feel the smile becoming real and your view of life becoming happier and more positive.

Celebrate - Dance - Sing:
Dance to happy music. Sing a happy song. Or just listen to upbeat music. The rhythm of happy music is primal. It works. Try it.