Look at the small things: a good cup of coffee, a bird visiting the garden, being able to hang the laundry outside. Bigger things will follow but start small.
I give you credit for recognizing your behavior. Start acknowledging your small blessings. Be thankful every morning to be given another day. Make an effort to do one thing nice for another person. Acknowledge to yourself the kindness you extended. You will see that kindness will get repaid. You will start to see gratitude become an import aspect of your life. It’s a circle of positivity and it starts with small steps.
When I'm being grateful and my mind keeps trying to come up with all the "Yeah, but's", I just find something positive to counter it. If I'm starting a thought on how grateful I am to have food and my brain says, "Yeah, but you didn't have enough to get everything you wanted." I just come right behind it and say loud in my mind or out loud that I'm grateful that I have the means for food. If I'm trying to be grateful for my loved ones and my brain says, "Yeah, but what about that loved one who's gone?" I just come right behind and state how thankful I am to still have time on this earth with the ones who are still here with me. Life can be hard and sometimes when we're thinking about good things, bad things will pop up all on their own without you trying. Rather than feel bad about it or dwelling on the sadness or despair that's in the "Yeah, but", be deliberate in always having a counter punch. Even if you feel like you're forcing the gratitude at first, like you're fighting for it, keep going! Having gratitude has to be a deliberate and conscious effort and fighting our own negative thoughts is a part of that. Good luck!
Think about something you take for granted (the fact that you can read, your smartphone, your health) and vividly imagine losing that thing forever. This helps you appreciate how they enhance your life every day
To be honest, I also don’t always *feel* positive when I am writing down my gratitudes, or saying my reasons out loud. But it doesn’t mean I am not grateful for them. Keep writing things down so you have a list, and you may find that reading the list when it’s up to 25 or so helps you become more positive. It’s definitely a work in progress for me!
Start small, imagine a cold shower instead of a hot one, imagine where that clean what comes from and what it would be like without it. Imagine you didn't have Home and what it would be like to shower in a public gym or truck stop. Humble yourself and gratitude while come naturally.