I used to get them once a month or two, now I haven't seen them in over a year. I'm not sure if they were just blanket knocking on all doors in the complex, or they pick me out of list somewhere. I'm a non-practicing member and I just simply don't care enough to remove my name from the records, but I'd like to know what makes them decide to knock on which door.

Missionaries who are sick of tracting will sometimes go over the ward roster. Inactive members are far more receptive than cold calling non-members. Even if you can't get the members back, at least you can spend a few pleasant hours doing some work that is better than getting the door slammed in your face.

If you are still on the ward roster, they may still show up. If the ward has sent your name back to SLC as lost, then the local missionaries will only show up if they randomly knock on your door tracting.

you usually get ratted out by your relatives.

I think they have access to DMV records. I've had them show up after changing my address and my parents swear they don't give them my info.

It's not random either because they know my name when they show up.

Fucking Cult.

They are guided by perspiration...

It depends on where you are, but the missionaries in my ward (who I used to go tracting with in preparation for my mission) had different maps which was passed down through missionaries.

They had one which was simply where the most recently tracted areas in the ward boundaries were highlighted. The missionaries would do an area which wasn't highlighted, then they'd highlight it and do another non-highlighted area and so un, until they'd gone over the whole are where they'd start again (it was a big place so it took over a year for them to get through the whole thing).

They had another which was of inactive members and former investigators. Where they lived was highlighted and there was a list attached with their exact addresses, so missionaries would know which places were "notable", or houses to look out for when tracting. So it's possible you might be on a list/map similar to this that the missionaries use.

The missionaries would sometimes pray over which street to go down.

Also people in the ward can suggest an address or a road for the missionaries to tract down. My ward actually implemented a system where the members could suggest addresses anonymously (I think they did that because members often didn't want missionaries going to people's houses and saying "so-and-so sent me here to talk to you", so doing it anonymously prevented that). It's possible that your address/road kept being suggested to the missionaries.

If I am in the bathroom, turn off all the lights, then stand in front of the mirror and say "Pay Lay Ale" three times, the missionaries knock on my door.