Make yourself comfortable in a position you won't feel the need to change and that won't distract you. Some people suggest keeping your eyes open and facing a blank wall, but that's never done it for me. Once you're comfortable, focus on your breathing. Keep a steady rhythm - I personally gravitate towards a six-count in and out, but I have no real idea why or what works for different people.
The difficult part is to then try and consciously relax. Every time you realise you're thinking about something, go back to focusing only on your breath. I personally can never
actually clear my mind - there's always something running through the back of my head - but I can at least put the brakes on most conscious thought.
Any time I try and completely empty my mind or think about nothing at all I find it to be a fool's errand because I start to think about thinking about nothing and it gets weird and annoying, so I just stick with resetting to the breath pattern instead. It's enough of a hook for my focus to stop it wandering too far, but not so much that I'm having to think hard about it.
YMMV. This is my experience from... I dunno, a decade or more of trying to meditate and never getting it to work quite as down pat as people seem to suggest is easy. Perhaps I shall never ascend unto nirvana as the Buddha did, but that's fine by me because I'm not a Buddhist.
Handy alternative breathing regulation tool:
https://ibb.co/cxNDAy