A common issue in WoW is “tunneling.” Don’t be that guy who has all the cool mods that adds indirectly to this problem. As we’ve all known even a few seconds distraction can kill you on some game mechanics. Turn off things you don’t need to raid with. Take some time to set up your mods right and turn off alerts you don’t need to see. I advise Bigwigs over Deadly Boss Mods because out of the box BigWigs has a lot of these unnecessary alerts turned off.
There comes a point in your UI that too much information can be overwhelming and you “have to tunnel through it all” until you miss that one important thing. A common philosophy in my UI/addon set up is “if I need to know about it or react to it” then it’s there and it’s prominent. If I don’t then it’s not. Things I care less about are in the corners of the screen like my dps/healing meter and world marker flares.
Make sure you have a clear viewable area around your character so you can see ground effects.