Well it depends on the river.. There arent many where you cant find stepping stones or a bridge.. I can count the ones I have had to wade on one hand..
if I have to wade, it is best to have some kind of shoes on your feet, be it crocs, flip flops or just your boots (with socks and foot beds removed and dry in the rucksack). Try and look to the far bank instead of at your feet
Like I say though, that is a very rare occurence. Mostly there are rocks or a split in the river or something that facilitates a crossing. In spate, your poles not only help with the pressure of the water, but also good for finding rocks just below the surface obscured by white water..
At the end of the day, unless the rivers are raging in spate, the worst that would happen if you get it wrong is you get a wet foot - not worth getting yourself worried or stressed about really