When you want to download, you also see the status of the person you are downloading from... I mean how many slots he has free...
Select the ones preferably with open slots or those with the least number of people in queue
For the purple ones, you can right click then and click on enter remote queue.
but I wouldn't recommend this as this means you'll ahve to wait for a long time (sometimes even days) for your download to start. Better get another source or start anothe file.
Another note: Do ensure that you have atleast 100 files shared. Otherwise people use programs that will automaticially remove you and prevent you from downloading from them. (Usually most people set it between 10-50 but 100 is on the safe side
)
Cheers