PIN codes are sent randomly by disney through either email or through standard mail. I don't believe there is any sort of pattern they go by and as far as I know, there isn't anything you can do to secure one. You can call to find out if one is attached to your name, but other than that, that's about all you can do besides wait to see if one shows up in your mailbox.
I have been going to Disney every year or so for 20 years. I have received only 1 PIN and that was 15 years ago. My nephew, who has been there a total of 3 times got one recently for a great rate at the Poly. Go figure. I am thinking that because they know I am coming anyway there is no need to entice me. I however think that maybe my loyalty should be rewarded every now and then. LOL