Forcing yourself to be thankful won't help. If you're in dire straits, maybe being grateful that things aren't worse than they are might be the best you can muster at any particular moment. Then, you build from there. Perhaps try being grateful that you live in a country where you have the right to vote or for indoor plumbing, friends, family, etcetera.
You will gradually become more and more self aware and grounded in what's right in your world.
Things to be grateful for:
Neuroplasticity refers to the brain's ability to rewire itself. Not only does this occur when parts of the brain have been damaged, but training yourself to think new thoughts that trigger different emotions is another example:
The following thirty minute video has a two minute section starting at the 16 minute mark telling that "neurons that fire together wire together" and that focusing on gratitude, love and joy can gradually make these more prevalent in our lives through neuroplasticity:
It, also, tells that changing yourself begins by "accepting your reality as it is, as it ACTUALLY is. But you experience it at the root level of sensation at the vibratory or energetic level without prejudice or influence of thought. Through sustained attention at the root level of consciousness the wiring for an entirely different perception of reality is created.
"Furthermore, circumstances don't matter, only your state of consciousness matters. Meditation in Sanskrit means to be free of measurement. Free of all comparison. To be free of all becoming. You are not trying to become something else. You are okay with what is.
The way to rise above the suffering of the physical realm is to totally embrace it. To say yes to it. So it becomes something within you rather than you being something within it.
How does one live in such a way that consciousness is no longer in conflict with its content. How does one empty the heart of petty ambitions? There must be a total revolution in consciousness. A radical shift in orientation from the outer world to the inner..... by accepting reality as it is!!!!"
My Comment: Using "as it is" as an introductory focal point for your meditative process might help.