I'm no expert on the Sith, but I notice that Palpatine/Sidious was recruited directly by Plagueis. In other words, he wasn't a Jedi, but was a Force-sensitive from the general population, but both Vader and Luke are Jedi Knights when recruitment attempts are made.
Is there a process or style that tends to show up in Sith recruitment? Is it easier to turn a Jedi, who has knowledge of the Force and basically needs to be made angry enough to start tapping into the dark side? Or are the Sith more likely to find someone who is strongly Force sensitive and more easily persuaded to turn to the dark side because of the morals and ethics used in Jedi training?
From what I see, it seems few Sith are former Jedi, other than the ones we've seen in the movies, but there's so much on the Sith, it's hard to tell.
(This also might hinge on whether the Sith find it easier to instruct one who does not know how to use the Force or easier to turn a Jedi to darkness if he does know the Force.)
Or are there other factors that influence how Sith pick their apprentices or who they'll train in the dark side but not make into a master (like Asajj Ventress, for example)?
Is there any general rule or procedure the Sith follow for recruiting? And, for the most part, once the Sith pick someone, are they usually successful in turning them to the dark side, or are there a lot of people who have the strength to avoid the dark path?