Monsters only die that fast till about lvl 25/30, unless you're in a really good group
You should have plenty of time to aim monsters after that
The 2 things that matter the most are your mouse and your internet connection. Make sure you're using a mouse you're comfortable with if you have a problem with yours. Sometimes the game is laggy and nothing will help there, BUT that doesn't mean should have 2 times less actions than you normally do
Check what monsters people are attacking first like BWconformity said and attack somewhere else if they are dying too fast. At any given point till around lvl 70, check if other people are attacking the same monster you are and if they are, switch to a monster noone is attacking, preferably one with high life. Every time someone starts attacking the same mob as you, switch again.
Important note: If you can't do enough normal attacks, you won't charge your abilities fast enough, so you have to learn to land as many normal hits as you can first
Important note 2: Spend your abilities points as soon as you get them ( if you don't for some reason )