Seems like such a simple thing to me. Look around for "No parking" signs. Glance at the placement of the other vehicles to get an idea of the generally accepted method of parking in that particular lot. Don't park in front of your neighbors driveway. Don't take more room than you need. Don't park in front of shop doors or loading docks. Easy.
At my shop, I have 5 parking spots, with lines painted. Seldom can people fit more than 4 cars in said holes, and if I have arranged three cars to leave two more spots, one car will park diagonally across those two spots.
Now I am an innocent bystander in a staff parking war between two businesses near me. I'm going to have to get the two guys together and treat them like the two year olds they are, or burn their buildings down so they both move.
/rant
Perhaps add arrows and directions to the painted lines?
Get a total beater and park precariously close to said offenders. Nothing short of a shotgun will scare them more than a rusty green 1978 Ford Country Squire parked two inches from their car.
SVreX
SuperDork
12/21/10 12:42 p.m.
Hire a dirty guy in a trench coat to beg from anyone who parks there and doesn't go into your place of business.
You'll have 5 empty spaces in no time. 
Post up a bunch of signs that mention "If you have information about car break-ins at this location please call this number" No one will park there ever again.
One of my next door neighbors at the office/warehouse place we rent had a habit of pulling in across three places sideways in the mornings. He did that until I pulled in behind him trapping him between my van and another parked car. I left that truck and climbed in one of the other ones and was gone for about an hour. I got phone calls ever fifteen minutes. He hasn't parked sideways in over two years now. Usually he's dead center between the lines. Not much is more aggravating than people that are too lazy to park correctly.
