I’m no expert or even experienced at meditation but what I have learnt from listening to hours of the ‘10% happier’ podcast that trying to stop your thoughts is impossible.
The main trick is to find stillness in the moments between your thoughts when you’re focusing on your breath and maybe your body.
Another great tip is to repeat in your mind over and over the following sentence; ‘I’m not my body and I’m not even my mind.’ It really helps to drown out any further thoughts. I learnt this from Sadhguru.
But when thoughts do come up, just acknowledge them and let them float away and refocus on your breath and/or that sentence.
Small steps, small steps.