I find giving the bead a wash over with some soapy water also helps. Thing about rubber is it is sticky, so tends to not slip over the rim as easily as you would want. As in many things, a bit of lube works wonders.
Thing also is once its been on once, it seems to stretch a little(may not be true but…)
I’ve really struggled to fit a tyre, then when finally got it to whoops of delight, i inflate(innertube user) and than have this delight smashed against the rocks when i find ive pinched the tube. But removing and refitting with a new tube i find is easier the 2nd time around.