so you get a scyther with nature you want, breed with ditto with speed iv and power anklet. get scyther with 31 iv in speed. get ditto with attack iv and power bracer, you have 1/2 chance of perfect speed and attack, with right nature since your scyther holds everstone. do same thing with hp/def/sp.def whatever next, eventually you'll get scyther with all three stats. next, you want ditto to hold destiny knot, eventually you'll get all four. the main goal is to get a male and a female with 5/6 perfect ivs. one with destiny knot and another with everstone to force the nature. once you have both like that you'll have about 1/~200 chance at a 6/6 one.
You can find some very good information on bulbapedia, among other places. They explain the EV system and even give a list of all the EVs. IVs are explained too, you can also check what was posted on this page and the one before by Austar.