The old faithful method I learnt years ago (from a VW Beetle manual) is to
tighten up the nut fairly snug and then try to move the washer sideways with
a screwdriver. If it does not move, its too tight.
Back off the nut a bit and try again. Once it can move sideways within its
side play, it's the right tightness.   Any tighter than that and the bearings
will fail quickly.

Cheers,   Steve