I read or heard somewhere that you push a sight into a dovetail from right to left and push it out left to right, as you are looking from receiver to muzzle. Is this accepted practice? I'm putting XS sights on my Ruger 77/357.

You should be able to tell which way it was driven in if you look closely then just drive it out whichever direction it came from.

I'm not aware of any standard in the industry.

Yes. In right to left; out, left to right. GD

What he said, but you might find an exception so don't go pounding away thoughtlessly. The idea is the dove tail is tapered for an easy start and tightens up when the sight gets close to center.

Any way to measure the taper with calipers?

A 6" machinist's ruler works well but can measure with the inside measurement side on your caliper. Actually anything can be a gauge if all you care about is which side is bigger.