There are a few ways some more complicated then others, you could use color finding and find the player and mouse to him/her or something with the chance of missing some players etc, you could watch for movement (more difficult), You could use Reflection to get the players and right click them if they are on your mainscreen and possibly add a boolean to it for if you have all ready clicked on them [The most accurate, probably the easiest]
Current Project: Catching up on what I missed, re-writing some old includes I done in the past.
Upcoming Project: Open For Suggestions