Misty Step is a great spell, but it has a tendency trip me up.
The first way happens at the beginning of a fight where my party is ambushed. My spellcaster needs to get out of dodge, so I select Misty Step. Then I survey the battlefield, looking for good spots to teleport. Then I start planning ahead, looking over all the enemies and potential ways to use the terrain. Then I forget MIsty Step was selected and I click somewhere on the map and my caster teleports somewhere awful and I cry.
I may be the only doofus this happens to, but it would help me a lot if the mouse cursor changed when Misty Step was selected, the way it changes for a ranged attack.
The second way I get tripped up is that the game doesn't really tell you when an offscreen character will have to move to get vision before casting Misty Step. If the character is onscreen, then you'll clearly see a white outline of where that character needs to stand to cast that spell. But Misty Step requires the camera to move away from the character, and you can't always have both target and character in frame at the same time. I've unknowingly triggered more attacks of opportunity than I care to count this way.
I don't really have a solution for this. Maybe the mouse cursor could change color if your character is about to trigger an attack of opportunity?