What helped me on this was understanding that the tyre gets clinched to the rim by the tube (well, unless you're running tubeless) and then understanding that you need a fixed point on the wheel to work out from.

For the latter, I usually go opposite from the valve to work my way to it on both sides and I found it a lot easier when I understood it as removing / fitting the tyre from one point to another rather than all at once, basically.

Also put a bit of air into your tube to help with refitting.