I have been playing for a month or so now, i have 1580-1600 psr, i have a good kda per match(5/3/6-7) I can deny like 10-20 in a normal match, my only problem is that sometimes in a teambattle, i get lost in all the flashy effects and basically get confused. i always get flamed for not stunning etc. Any help would be appreciated, thanks.
Basically, it depends on the current length of the game(how early is the battle, level 6-7,8-10,11-16?), depends on the opposite team, depends on your team...(if you're asking on who to stun)
Theres so many possibilities and you have to adjust accordingly during the team battle.
As for the effects, you can turn most down or just plain off and play the game as "raw" as it can get.
Stun them!! Really, you just have to learn to see what's going on. If you say have an AOE stun like Pebbles, you might want to throw that in in the big pile of enemey heroes. Or try to look for someone who is channeling an ulti, always nice to cancel those.
The same thing happened to me when I started, but being an avid DotA player I was able to get used to it quickly. My only tip is to try and concentrate on your hero during team fights, while also focusing on who you intend to target.