This should be an interesting thread
Usually I put the backing plate shoe side up in the vice , grippedd by the anchor stay bolt
Put the springs on each shoe with them vertical and the ends of the shoes against the cam & pivot
Then press down on the shoes while pushing them apart
Helps if you do this bit quickly
Now lets see how every one else does it
Sure to be a dozen different ways
I don't ever recall using a vice, but yep, pair the shoes up with the springs, hold them more or less vertical and push downwards and out...although if the cam has a large diameter retainer, it can be easier to allow one shoe to sit fully home before levering the other over.
If I find them a fight, I remove the fixed and pivot pins from the brake plate.
Then fit the pins to the shoes.
That assembly is then refitted to the brake plate.