There is a mod to limit opponent idle animations:
Stand Still When I Attack.
Otherwise, zooming in, aiming for the feet (when possible) or switch to the overhead tactical view can help.
For skills/spells you can use the turn order portraits at the top of the screen to target.
For normal attacks, right click an opponent and select Attack (no effect if you miss) or hold the Shift button down to queue commands and left click: if you get a red target selection indicator, release the Shift button, otherwise if you get the white move indicator, right click to cancel.
That could be cause by a stat debuff, leaving the character without the requirements to equip the item.
Click on rats from farther way, rather than trying to get close and then click on them.
