Your mouse should almost always be on the party/enemy list

This is my biggest tip for ranked climbing tbh. Adjust your hud so all 10 players are in a row. You should constantly be paying attention to everyone's health bars, mana bars, limit break bars, and targeting from the player list is infinitely easier than clicking on them or tabbing to them. You should also be calling targets as you do this with a macro, focusing on people with less mana or people you've seen guard recently, and respecting enemies with their limit breaks ready or almost ready. This is the macro I use for calling the target to attack:

/micon "Attacking Target" quickchat
/quickchat "Attacking Target"
/mk attack1 <t>

And then to quickly target the marked target I just use

/target <attack1>

I have the former bound to shift+R and the latter bound to R.

I don't play on controller but if I had to take a swing at it i'd recommend making targeting macros to target players 1-10 on your cross hotbars, or at the very least your five enemies.