Thanks for this! This is a really good read and also makes you feel much better

Thanks for this! IT was indeed a very good read

I think the way I would practice is meditation. That really helps you keep positive in life

The other way would be to not attract passimism in thought processs by suppressing your sub-concious mind

Genetically, we're selected to be negative when in a hostile environment.  The caveman who pessimistically  saw a tiger behind every bush tended to live longer than the one who gathered flowers and gazed on the beauty of the clouds when walking.
Add to this that from a gene's point of view, men and women are a way of passing genes into the next generation (The Selfish Gene and the Moral Animal; Robert Wright).  A discontented person strives harder at everything in life.
One of the problems in this life of genetic tendencies is that they are no longer useful in our modern lives.  The person who retrains their thinking to perceive positives, to view their needs met and be grateful for anything in excess of that, as contrasted with the person who thinks negatively and focuses on unmet wants, lives longer, with better quality of life.

For those who enjoy a more technical view of the process, here it is.  This may be skipped.
The physiological process goes beyond "positive thinking".  The bulk of the brain's emotion/thought/perception process is isolate.  The brain floats in isolation, and it doesn't actually know, for the most part, if something is being experienced, or modeled in the forebrain (neo-cortext).  This is one reason visualization exercises and mediation work so well in training thoughts and in learning to exercise.  So well, in fact, that professional athletes and Olympian regularly use visualization.

The normal process is that nervous stimulation comes into the Reticular Activating System (RAS) at the base of the brain.  It is the filter that determines what is passed on, and what isn't.  The RAS is what allows you to wake up, and what says a meeting is boring and suggests sleep.  It is at the very foundation of the system, but can be trained over time - if you stopped wetting the bed, it is because you trained your RAS that waking up to avoid social embarrassment was more important than sleeping when your bladder told the RAS it was full.  Strychnine eliminates the RAS ability to filter - and the mammal dies because it can't ignore its own deep muscle sounds moving on one another, its breathing, heartbeat, and all the other feedback the body gives, as well as external sensations, and dies in convulsions from over-stimulation and lack of sleep.
From the RAS, the sensations go to the centers of emotion and get an energy charge of "importance" determined by the strength of the input and prior experience.  It then goes to the Cortex for an emergency check.  If the Cortex determines that there is time, it will pass it to the Neo-Cortex for modeling and decision, to be sent back down the chain.
An example for understanding.  
Your hand rests on the glass stove and the nerves send an enormous charge up the slow-fiber nerve bundles, far stronger than the fast-fiber ones, and it reaches the RAS first, signaling pain instead of sensation.  It is immediately passed to the thalamus and such and given a large strength and sent on to the Cortex.  The Cortex says, 'HOT!' and sends back down the chain "jerk away!".   So before you had a chance to "think" (Neo-Cortex), your hand has jerked back from the stove.  Make sense?

Now, the Neo-Cortex is responsible for programming the rest for environment and situations beyond the simple.  It is a slow process, takes about 40 days more of less for the situation to reach the RAS and re-tune its rules for filtering.  Here's an example of how it works:
You hate your job.  You particularly hate your boss.  He's always riding you, you never feel like you're good enough, and you're afraid of being fired any day.  You have debts, mouths to feed.  You pass down day after day thoughts as you brood that this job is life or death.  You dwell on emotions and thoughts that make this essential.  You program all the way to the RAS.
You come in after a few weeks, are called into the manager's office, and the last thing you hear is "you're being let go" - and testify to that in court.
Your RAS heard that - and sent it right on because you've identified this long before as an emergency.  It picked up the preprogrammed emotional charge waiting for it, and hit the Cortex, which heard and reacted to save your life and your family's lives - by eliminating the threat.  The Cortex ALWAYS exists in an eternal now, and doesn't consider consequences - that was the job of the Neo-Cortex, and you did it for weeks with your thinking.

So positive thinking is a way of controlling your thoughts until they "become habit".  Of dwelling on positives, on gratitude, on needs met instead of wants unmet, until you've trained your Cortex out of emergency hijacks, and trained your RAS to recognize positives and send them up, and to filter out the minor negatives.  After the training period, in that way, it becomes a self-enforcing cycle.