Not something I wish I knew, but something I accidentally found out;
- You can shoot levers to open/close them

Also do not underestimate the utility of all the various "
Apply Effect On Hit" items, because you can create a debuff-monster that entirely crowd-controls enemies just by smacking them.
An example of Karlach's (Tiger Barb) numerous debuffs completely locking down bosses just by smacking them with a stick and making a joke out of them;