Here are videos for every mission with a Silent Assassin rank on each. I followed these guides and they helped a lot!
All credit goes to srfgaming for making the videos!!
EDIT: I've been told some people have been having trouble with the second mission. On the video at the beginning srfgaming doesn't close the doors on the van you start in and this causes him to get an alert that a dead body has been found. If you're having trouble getting Silent Assassin rank try closing the doors of the van by using the button just outside of it. This should help. Thanks to Devonian AUS for pointing this out.