This isn't really embarassing for me but it's probably the most surprising for you so here goes.

When I was originally leveling up I obviously had the default keys set on most things, meaning as I learned new skills they soon became troublesome to hit if I wished to retain the ability to move at the same time. Most people, as I've later realized, handle this by changing their keybinds to keys that are always within reach. I couldn't say at what point I fully switched to doing it but my solution was to just to let go of my mouse and get a second hand on the keyboard.

This is how I still play to this very day. Inside instances I only touch my mouse if a boss jumps and I need to look around to see where they are charging from, as during those moments I'm not losing anything from removing my right hand from the keyboard either. One current exception is E7S that forces me to use my mouse for facing my teleport the correct way but since it's during a simple 1-2-3 portion of my rotation it doesn't cost me anything.