To Create A Perfect Mary Sue

We've all seen them, those characters that have everything, lack nothing, and we utterly despise them. Yeah, THOSE characters *coughBellaSwancough* Well, I'm going to go through and try to give a better understanding of a Mary Sue, and well, through how to write one, I'll give you tips on avoiding Mary Sues...or Gary Stus, if you're into that kind of thing.