A part of being a stoic is exercising gratitude of the things that were given to you and the things that weren't taken away from you - things that are out of your control. But you don't have to be a stoic if that's not your cup of tea. You can keep a gratitude diary regardless of which philosophy, if any, you follow.
I cannot be 100 % sure about this, but chances are you did nothing to earn your existence in this universe. The chance to live, breath, and do whatever your want to do, was given to you - no questions asked. It would seem arrogant not to be grateful for the opportunity.
Because let's face it - if you really loathed life and felt wrath towards whoever or whatever caused your existence, you could just end your life. But you're not ending your life, so obviously you enjoy life, at least to some extent. So be grateful.
You can write down your gratitudes on your computer, but I definitely recommend doing it by hand. Writing with a pen has something extra to it - something more personal than merely typing on a keyboard. So get a special notebook for your gratitudes alone (you can also get a special pen), and depending on your preference, every morning or every night, write down what you're grateful for. You can address a chosen entity, or not - it doesn't matter. You can use a list form or write in full sentences, however you like. The point is that you think about what you're grateful for.
That way, every day is a little Thanksgiving.
Here's an example, partly a rather general one but one nonetheless:
Thank you universe! November 11th 2018
I'm grateful for my health - I'm in my best shape in years.
I'm grateful for my day job and for my ability to produce for my own company. Doing both gives me meaning and immense joy.
I'm grateful for my relationship with my spouse and with my family. I'm grateful for their health as well.
I'm grateful for the opportunity to do whatever I want with my life.
I'm grateful for my freedom.
I'm grateful for the things I still have to experience and the years of life I still have ahead. I'm also grateful for everything I've experienced so far.
I'm grateful for the wonderful foggy weather of today!
I'm grateful for the insane work flow I've been having all day so far.
I'm grateful for life, and looking forward to tomorrow with gratitude and eagerness to find out what it shall bring.
Doing this every day is sure to increase your happiness, meaning in life, mental health, and the belief that the world is on your side, if you just choose to see it that way.
Oh, and gratitude of course.